US Geologist - University of Sindh Geologists

SOLAR SYSTEM

The earth and everything that orbits around the sun, including the eight planets and their satellite; the asteroids and comets; and interplanetary dust and gas. The term may also refer to a group of celestial bodies orbiting another star.

                       DIMENSION: The dimensions of the solar system are specified in terms of the mean distance from Earth to the Sun, called the astronomical unit (AU). One AU is equal to 150 million km (about 93 million mi).

THE SUN & THE SOLAR SYSTEM: The Sun is a typical star of intermediate size and luminosity. Sunlight and other radiation are produced by the conversion of hydrogen into helium in the Sun’s hot, dense interior. Although this nuclear fusion is transforming 600 million metric tons of hydrogen each second, the Sun is so massive that it can continue to shine at its present brightness for 6 billion years. This stability has allowed life to develop and survive on Earth.

 

“The Sun is so massive that it can continue to shine at its present brightness for 6 billion years.”

 

Our Solar System is the part of Milky Way Galaxy. According to the scientists there are billions of several Solar System in one Galaxy and there are billions of other Galaxies in this UNIVERSE.

UNIVERSE: This  inflationary theory was develop in the 1970s to solve several mysteries still remaining in the universe as it was described by the big bang theory. Astronomers accept the theory that about 14 billion years ago the universe began as an explosive event resulting in a hot, dense, expanding sea of matter and energy. This event is known as the big bang.

GALAXY: A massive ensemble of hundreds of millions of stars, all gravitationally interacting, and orbiting about a common center. Astronomers estimate that there are about 125 billion galaxies in the universe. All the stars visible to the unaided eye from Earth belong to Earth’s galaxy, the Milky Way.

MILKY WAY GALAXY: The large, disk-shaped aggregation of stars, or galaxy, which includes the sun and its solar system. In addition to the Sun, the Milky Way contains about 400 billion other stars. There are hundreds of billions of other galaxies in the universe, some of which are much larger and contain many more stars than the Milky Way.

 

In our Solar System there are eight planets and one star name Sun. Our Solar System also includes several of asteroids and meteoroids. Eight Planets of Solar System devided into two parts                  (a) Inner planets   (b) Outer Planets

 

                   INNER PLANETS                                                                OUTER PLANETS

(i)                  Mercury                                                                    (i)          Jupiter

(ii)                Venus                                                                        (ii)        Saturn

(iii)               Earth                                                                          (iii)       Uranus

(iv)              Mars                                                                           (iv)       Neptune

 

INNER PLANETS: The inner planets are those planets which are closer to the sun and they are small in size and are composed primarily of rock and iron.

 

OUTER PLANETS: Outer planets are those which are far away from the sun and they are all huge in size and consist mainly of hydrogen, helium, and ice.

 

STAR: Any object that can produce its own light and energy. Our SUN is the only star in our Solar System and SUN contains 99.86% mass of our Solar System.

PLANETS: A planet is that which should have three qualities. They are,

(a)    Planet should revolve around the sun.

(b)   Planet should have spherical shape.

(c)    Planet should clean its surrounding.

SATELLITE: Satellite is that body which revolves around the Planet.

ASTEROIDS: Asteroids fulfils only one condition of PLANETS. That is it revolves around the sun. It also have two more qualities whish are not similar from Planets which are they have very small mass and they don’t take spherical shape.

METEOROIDS: All objects that falls upon the surface of the earth called Meteoroids. They don’t move in particular orbit.

COMENTS: They have angular path mostly made up ice or crystal. Whenever they get closer to the sun they sublimate (converted into different gases). Forming a tail revolving around the sun in angular orbit with respect to the other planets.

 

                                    EIGHT PLANETS OF THE SOLAR SYSTEM

 

MERCURY: Mercury orbits closer to the Sun than any other planet, making it dry, hot, and virtually airless. Although the planet’s cratered surface resembles that of the Moon, it is believed that the interior is actually similar to Earth’s, consisting primarily of iron and other heavy elements.

 

VENUS: Venus is the brightest object in our sky, after the sun and the moon. Swirling clouds of sulfur and sulfuric acid obscure Venus’s surface and inhibited study of the planet from Earth until technology permitted space vehicles, outfitted with probes, to visit it. These probes determined that Venus is the hottest of the planet, with a surface temperature of about 460º C (about 860º E). Scientist believe that a greenhouse effect causes the extreme temperature, hypothesizing that the planet’s thick clouds and dense atmosphere trap energy from the sun.

 

EARTH: An oxygen-rich and protective atmosphere, moderate temperatures, abundant water and a varied chemical composition enable Earth to support life, the only planet known to harbour life. The planet is composed of rock and metal, which are present in molten form beneath its surface.

 

MARS: The most detailed information available about Mars has come from unpiloted spacecraft sent to the planet by the United States between 1964 and 1976 from this data, scientists have determined that the planet’s atmosphere consists primarily of carbon dioxide, with small amount of nitrogen, oxygen, water vapor, and other gases. Because the atmosphere is extremely thin, daily temperatures can vary as much as 100 Celsius degree (190 Fahrenheit degree). In general, surface temperatures are too cold and surface pressure too low for water to exist in a liquid state on Mars. The planets resemble a cold, high-altitude desert.

 

JUPITER: Jupiter is the largest of the planes, with a volume more than 1,300 times greater that of Earth. Jupiter’s colorful bands are caused by strong atmosphere currents and accentuated by a dense cloud cover.

 

SATURN: Saturn, distinguished by its rings, is the second largest planet in the solar system. This processed Hubble Space Telescope image shows the planets could bands, storm and rings as they would appear to the human eye.

 

URANUS: Uranus’s blue-green color comes from the methane gas present in its cold, clear atmosphere. The dark shadings at the right edge of the sphere correspond to the day-night boundary on the planet. Beyond this boundary, Uranus’s northern hemisphere remains in a four-decade-long period of darkness because of the way the planers rotates.

 

NEPTUNE: Neptune is the major planet in the solar system. Neptune maintains an almost constant distance, about 4.5 billion km (about 2.8 billion mi), from the Sun. Neptune revolves outside the orbit of Uranus Astronomers believe Neptune has an inner rocky core that is surrounded by a vast ocean of water mixed with rocky material. From the inner core, this ocean extends upward until it meets a gaseous atmosphere of hydrogen, helium and trace of methane.         

MINERALS: DEFINITION, PROPERTIES AND OCCURRENCES

The Science of Mineralogy

The science of mineralogy is the study of the physics and chemistry of natural, solid, crystalline materials.

1 - The origin of the chemical elements

The Universe that we perceive is thought to have begun in a “Big Bang” approximately 15 billion years ago. This cosmic explosion produced among other particles, protons, neutrons, and electrons which rapidly became organized into the elements hydrogen (1 proton, 1 electron), and helium (2 protons, 2 neutrons, and 2 electrons), plus trace amounts of deuterium (1 proton,1 neutron, and 1 electron), 3He (2 protons, 1 neutron, 2 electrons), and lithium (3 protons, 3 neutrons, 3 electrons). Most of the mass of this primordial material is carried in the protons and neutrons (baryons), each of these particles being approximately 1800 times more massive than an electron.

As the gas of these primitive elements expanded, gravitational instabilities caused parts to co alesce into huge clouds that eventually became galaxies and clusters of galaxies. Further, gravitational instabilities within each galaxy caused further collapse of the gas into primitive stars where the very high temperatures caused by gravitational collapse ignited the fires of thermonuclear fusion in which the nuclei of the primitive light elements combined to form heavier elements. In the largest of these stars, the fusion reactions proceeded in stages producing successively heavier elements. The final reaction in which Si combines to form Fe proceeds so rapidly once ignited that the star explodes in what we call a supernova. Our own solar system coalesced from the remnants of one or more of these supernova explosions.

As the gas that formed our solar system collapsed from gravitation it formed a rotating disk of gas that first heated and then cooled. As the gas cooled the heavy elements began to precipitate solid particles of dust. The first precipitates were crystals (minerals) of platinum-group metals, Os, Ru, and Ir, followed by aluminum oxides, metallic nickel-iron, and Mg silicates. This was followed by more complex silicates, then various sulfides of heavy metals. We can see this precipitation sequence preserved in primitive meteorites. Before temperatures cooled sufficiently in the inner solar system so that the most volatile elements (H, C, N, and the noble gases) could condense, H fusion in the sun ignited and blew these elements to the outer solar system where they are enriched in the outer planets, Jupiter, Saturn, Uranus, and Neptune.

The Earth accreted from these early solid particles called chondrules, and these refractory elements are enriched in the Earth relative to their abundance in the Sun. As the proto Earth grew from the influx of solid particles it got hot enough to melt so that the dense Ni-Fe metal together with elements soluble in the metal sank to the center and formed the core, and the lighter oxygen-bearing minerals (mostly silicates) formed the mantle. Today the mantle is entirely solid and has been throughout most of Earth’s history, whereas the core comprises a liquid metal outer core and a solid metal inner core.

So, except for the oceans and atmosphere, the Earth today is made up of solid minerals to a depth of about 2900 km. The physics and chemistry of the solid phases of the Earth control much of the physics and chemistry of our environment. Unlike fluids, minerals preserve the records of Earth’s history. Further minerals contain the wealth of natural resources of the planet. Therefore understanding the physics and chemistry of the solid materials of the planet (mineralogy) is central to much of the Earth Sciences.

Definition of a Mineral

A mineral is a naturally-occurring, homogeneous solid with a definite, but generally not fixed, chemical composition and an ordered atomic arrangement. It is usually formed by inorganic processes.

Let’s look at the five parts of this definition:

1.) “Naturally occurring” means that synthetic compounds not known to occur in nature cannot have a mineral name. However, it may occur anywhere, other planets, deep in the earth, as long as there exists a natural sample to describe.

2.) “Homogeneous solid” means that it must be chemically and physically homogeneous down to the basic repeat unit of the atoms. It will then have absolutely predictable physical properties (density, compressibility, index of refraction, etc.). This means that rocks such as granite or basalt are not minerals because they contain more than one compound.

3.) “Definite, but generally not fixed, composition” means that atoms, or groups of atoms must occur in specific ratios. For ionic crystals (i.e. most minerals) ratios of cations to anions will be constrained by charge balance, however, atoms of similar charge and ionic radius may substitute freely for one another; hence definite, but not fixed.

4.) “Ordered atomic arrangement” means crystalline. Crystalline materials are three-dimensional periodic arrays of precise geometric arrangement of atoms. Glasses such as obsidian, which are disordered solids, liquids (e.g., water, mercury), and gases (e.g., air) are not minerals.

5.) “Inorganic processes” means that crystalline organic compounds formed by organisms are generally not considered minerals. However, carbonate shells are minerals because they are identical to compounds formed by purely inorganic processes.

An abbreviated definition of a mineral would be “a natural, crystalline phase”. Chemists have a precise definition of a phase:

A phase is that part of a system which is physically and chemically homogeneous within itself and is surrounded by a boundary such that it is mechanically separable from the rest of the system.

The third part of our definition of a mineral leads us to a brief discussion of stoichiometry, the ratios in which different elements (atoms) occur in minerals. Because minerals are crystals, dissimilar elements must occur in fixed ratios to one another. However, complete free substitution of very similar elements (e.g., Mg⁺² and Fe⁺² which are very similar in charge (valence) and radius) is very common and usually results in a crystalline solution (solid solution). For example, the minerals forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄) are members of the olivine group and have the same crystal structure, that is, the same geometric arrangement of atoms. Mg and Fe substitute freely for each other in this structure, and all compositions between the two extremes, forsterite and fayalite, may occur. However, Mg or Fe do not substitute for Si or O, so that the three components, Mg/Fe, Si and O always maintain the same 2 to 1 to 4 ratio because the ratio is fixed by the crystalline structure. These two minerals are called end-members of the olivine series and represent extremes or “pure” compositions. Because these two minerals have the same structure, they are called isomorphs and the series, an isomorphous series.

In contrast to the isomorphous series, it is also common for a single compound (composition) to occur with different crystal structures. Each of these structures is then a different mineral and, in general, will be stable under different conditions of temperature and pressure. Different structural modifications of the same compound are called polymorphs. An example of polymorphism is the different minerals of SiO₂ (silica); alpha-quartz, beta-quartz, tridymite, cristobalite, coesite, and stishovite. Although each of these has the same formula and composition, they are different minerals because they have different crystal structures. Each is stable under a different set of temperature and pressure conditions, and the presence of one of these in a rock may be used to infer the conditions of formation of a rock. Another familiar example of polymorphism is graphite and diamond, two different minerals with the same formula, C (carbon).

Glasses (obsidian), liquids, and gases however, are not crystalline, and the elements in them may occur in any ratios, so they are not minerals. So in order for a natural compound to be a mineral, it must have a unique composition and structure. We will return in a few weeks to further discussion of stoichiometry and stability. The fourth part of our definition of a mineral, the part about the ordered atomic arrangement, leads us to a discussion of symmetry which will occupy our first few weeks.

Mineral Properties in Hand Specimen

Learning to recognize hand specimens of approximately 100 of the most common rock-forming minerals is an important part of this course. This recognition is based on seven easily examined properties plus a few unique properties such as magnetism or radioactivity that are strong clues to a mineral’s identity. These seven properties are:

1. Crystal form and habit (shape).

2. Luster and transparency

3. Color and streak.

4. Cleavage, fracture, and parting.

5. Tenacity

6. Density

7. Hardness

Crystal form and habit

Recognizing crystal forms (a crystal face plus its symmetry equivalents) in the various crystal systems is one of the reasons we spend some time in lab studying block models. The crystal faces developed on a specimen may arise either as a result of growth or of cleavage. In either case, they reflect the internal symmetry of the crystal structure that makes the mineral unique. The crystal faces commonly seen on quartz are growth faces and represent the slowest growing directions in the structure. Quartz grows rapidly along its c-axis (three-fold or trigonal symmetry axis) direction and so never shows faces perpendicular to this direction. On the other hand, calcite rhomb faces and mica plates are cleavages and represent the weakest chemical bonds in the structure. There is a complex terminology for crystal faces, but some obvious names for faces are prisms and pyramids. A prism is a face that is perpendicular to a major axis of the crystal, whereas a pyramid is one that is not perpendicular to any major axis.

Crystals that commonly develop prism faces are said to have a prismatic or columnar habit. Crystals that grow in fine needles are acicular; crystals growing flat plates are tabular. Crystals forming radiating sprays of needles or fibers are stellate. Crystals forming parallel fibers are fibrous, and crystals forming branching, tree-like growths are dendritic.

 

Luster and transparency

The way a mineral transmits or reflects light is a diagnostic property. The transparency may be either opaque, translucent, or transparent. This reflectance property is called luster. Native metals and many sulfides are opaque and reflect most of the light hitting their surfaces and have a metallic luster. Other opaque or nearly opaque oxides may appear dull, or resinous. Transparent minerals with a high index of refraction such as diamond appear brilliant and are said to have an adamantine luster, whereas those with a lower index of refraction such as quartz or calcite appear glassy and are said to have a vitreous luster.

Color and streak

Color is fairly self-explanatory property describing the reflectance. Metallic minerals are either white, gray, or yellow. The presence of transition metals with unfilled electron shells (e.g. V, Cr, Mn, Fe, Co, Ni, and Cu) in oxide and silicate minerals causes them to be opaque or strongly colored so that the streak, the mark that they leave when scratched on a white ceramic tile, will also be strongly colored.

Cleavage, fracture, and parting

Because bonding is not of equal strength in all directions in most crystals, they will tend to break along crystallographic directions giving them a fracture property that reflects the underlying structure and is frequently diagnostic. A perfect cleavage results in regular flat faces resembling growth faces such as in mica, or calcite. A less well developed cleavage is said to be imperfect, or if very weak, a parting. If a fracture is irregular and results in a rough surface, it is hackly. If the irregular fracture propagates as a single surface resulting in a shiny surface as in glass, the fracture is said to be conchoidal.

Tenacity

is the ability of a mineral to deform plastically under stress. Minerals may be brittle, that is, they do not deform, but rather fracture, under stress as do most silicates and oxides. They may be sectile, or be able to deform so that they can be cut with a knife. Or, they may be ductile and deform readily under stress as does gold.

Density

is a well-defined physical property measured in g/cm³.a Most silicates of light element have densities in the range 2.6 to 3.5. Sulfides are typically 5 to 6. Iron metal about 8, lead about 13, gold about 19, and osmium, the densest substance, and a native element mineral, is 22. Density may be measured by measuring the volume, usually by displacing water in a graduated cylinder, and the mass. Specific gravity is very similar to density, but is a dimensionless quantity and is measured in a slightly different way. Specific gravity is measured by determining the weight in air (Wa) and the weight in water (Ww) and computing specific gravity from SG = Wa / (Wa-Ww). In practice this is done using a Jolly balance as we will see in lab.

Hardness

is usually tested by seeing if some standard minerals are able to scratch others. A standard scale was developed by Friedrich Mohs in 1812 The standard minerals making up the Mohs scale of hardness are:

        1. Talc                        6. Orthoclase

        2. Gypsum                      7. Quartz

        3. Calcite                     8. Topaz

        4. Fluorite                    9. Corundum

        5. Apatite                     10 Diamond

This scale is approximately linear up to corundum, but diamond is approximately 5 times harder than corundum.

Unique Properties

A few minerals may have easily tested unique properties that may greatly aid identification. For example, halite (NaCl) (common table salt) and sylvite (KCl) are very similar in most of their physical properties, but have a distinctly different taste on the tongue, with sylvite having a more bitter taste. Whereas it is not recommended that students routinely taste mineral specimens (some are toxic), taste can be used to distinguish between these two common minerals.

Another unique property that can be used to distinguish between otherwise similar back opaque minerals is magnetism. For example, magnetite (Fe₃O₄), ilmenite (FeTiO₃), and pyrolusite (MnO₂) are all dense, black, opaque minerals which can easily be distinguished by testing the magnetism with a magnet. Magnetite is strongly magnetic and can be permanently magnetized to form a lodestone; ilmenite is weakly magnetic; and pyrolusite is not magnetic at all.

Other Properties

. There are numerous other properties that are diagnostic of minerals, but which generally require more sophisticated devices to measure or detect. For example, minerals containing the elements U or Th are radioactive (although generally not dangerously so), and this radioactivity can be easily detected with a Geiger counter. Examples of radioactive minerals are uraninite (UO₂), thorite (ThSiO₄), and carnotite (K₂(UO₂)(VO₄)₂ rH₂O). Some minerals may also be fluorescent under ultraviolet light, that is they absorb UV lighta and emit in the visible. (There is a display of fluorescent mineral on the first floor of the (old)Geology Building.) Other optical properties such as index of refraction and pleochroism (differential light absorption) require an optical microscope to measure and are the subject of a major section of this course. Electrical conductivity is an important physical property but requires an impedance bridge to measure. In general native metals are good conductors, sulfides of transition metals are semi-conductors, whereas most oxygen-bearing min erals (i.e., silicates, carbonates, oxides, etc.) are insulators. Additionally, quartz (SiO₂) is piezoelectric (develops an electrical charge at opposite end under an applied mechanical stress); and tourmaline is pyroelectric (develops an electrical charge at opposite end under an applied thermal gradient).

Mineral Occurrences and Environments

In addition to physical properties, one of the most diagnostic features of a mineral is the geological environment in which it is occurs. Learning to recognize different types of geological environments can be thus be very helpful in recognizing the common minerals. For the purposes of aiding mineral identification, we have developed a very rough classification of geological environments, most of which can be visited locally.

Igneous Minerals

Minerals in igneous rocks must have high melting points and be able to co-exist with, or crystallize from, silicate melts at temperatures above 800 º C. Igneous rocks can be generally classed according to their silica content with low-silica (<< 50 % SiO₂) igneous rocks being termed basic or mafic, and high-silica igneous rocks being termed silicic or acidic. Basic igneous rocks (BIR) include basalts, dolerites, gabbros, kimberlites, and peridotites, and abundant minerals in such rocks include olivine, pyroxenes, Ca-feldspar (plagioclase), amphiboles, and biotite. The abundance of Fe in these rocks causes them to be dark-colored. Silicic igneous rocks (SIR) include granites, granodiorites, and rhyolites, and abundant minerals include quartz, muscovite, and alkali feldspars. These are commonly light-colored although color is not always diagnostic. In addition to basic and silicic igneous rocks, a third igneous mineral environment representing the final stages of igneous fractionation is called a pegmatite (PEG) which is typically very coarse-grained and similar in composition to silicic igneous rocks (i.e. high in silica). Elements that do not readily substitute into the abundant minerals are called incompatible elements, and these typically accumulate to form their own minerals in pegmatites. Minerals containing the incompatible elements, Li, Be, B, P, Rb, Sr, Y, Nb, rare earths, Cs, and Ta are typical and characteristic of pegmatites.

Metamorphic minerals

Minerals in metamorphic rocks have crystallized from other minerals rather than from melts and need not be stable to such high temperatures as igneous minerals. In a very general way, metamorphic environments may be classified as low-grade metamorphic (LGM) (temperatures of 60 º to 400 º C and pressures << .5 GPa (=15km depth) and high-grade meta morphic (HGM) (temperatures > 400 º and/or pressures > .5GPa). Minerals characteristic of low- grade metamorphic environments include the zeolites, chlorites, and andalusite. Minerals character istic of high grade metamorphic environments include sillimanite, kyanite, staurolite, epidote, and amphiboles.

Sedimentary minerals

Minerals in sedimentary rocks are either stable in low-temperature hydrous environments (e.g. clays) or are high temperature minerals that are extremely resistant to chemical weathering (e.g. quartz). One can think of sedimentary minerals as exhibiting a range of solubilities so that the most insoluble minerals such as quartz gold, and diamond accumulate in the coarsest detrital sedimentary rocks, less resistant minerals such as feldspars, which weather to clays, accumulate in finer grained siltstones and mudstones, and the most soluble minerals such as calcite and halite (rock-salt) are chemically precipitated in evaporite deposits. Accordingly, I would classify sedimentary minerals into detrital sediments (DSD) and evaporites (EVP). Detrital sedimentary minerals include quartz, gold, diamond, apatite and other phosphates, calcite, and clays. Evaporite sedimentary minerals include calcite, gypsum, anhydrite, halite and sylvite, plus some of the borate minerals.

Hydrothermal minerals

The fourth major mineral environment is hydrothermal, minerals precipitated from hot aqueous solutions associated with emplacement of intrusive igneous rocks. This environment is commonly grouped with metamorphic environments, but the minerals that form by this process and the elements that they contain are so distinct from contact or regional metamorphic rocks that it us useful to consider them as a separate group. These may be sub-classified as high temperature hydrothermal (HTH), low temperature hydrothermal (LTH), and oxydized hydrothermal (OXH). Metals of the center and right-hand side of the periodic table (e.g. Cu, Zn, Sb, As, Pb, Sn, Cd, Hg, Ag) most commonly occur in sulfide minerals and are termed the chalcophile elements. Sulfides may occur in igneous and metamorphic rocks, but are most typically hydrothermal. High temperature hydrothermal minerals include gold, silver, tungstate minerals, chalcopyrite, bornite, the tellurides, and molybdenite. Low temperature hydrothermal minerals include barite, gold, cinnabar, pyrite, and cassiterite. Sulfide minerals are not stable in atmospheric oxygen and will weather by oxidation to form oxides, sulfates and carbonates of the chalcophile metals, and these minerals are characteristic of oxidized hydrothermal deposits. Such deposits are called gossans and are marked by yellow-red iron oxide stains on rock surfaces. These usually mark mineralized zones at depth and are very common in Colorado.

 

 

Classification of Minerals

Minerals are classified on their chemistry, particularly on the anionic element or polyanionic group of elements that occur in the mineral. An anion is a negatively charge atom, and a polyanion is a strongly bound group of atoms consisting of a cation plus several anions (typically oxygen) that has a net negative charge. For example carbonate, (CO3) 2-, silicate, (SiO4)4- are common poly anions. This classification has been successful because minerals rarely contain more than one anion or polyanion, whereas they typically contain several different cations.

1 - Native elements

The first group of minerals is the native elements, and as pure elements, these minerals contain no anion or polyanion. Native elements such as gold (Au), silver (Ag), copper (Cu), and platinum (Pt) are metals, graphite is a semi-metal, and diamond (C) is an insulator.

2 - Sulfides

The sulfides contain sulfur (S) as the major “anion”. Although sulfides should not be considered ionic, the sulfide minerals rarely contain oxygen, so these minerals form a chemically distinct group. Examples are pyrite (FeS₂), sphalerite (ZnS), and galena (PbS). Minerals containing the elements As, Se, and Te as “anions” are also included in this group.

3 - Halides

The halides contain the halogen elements (F, Cl, Br, and I) as the dominant anion. These minerals are ionically bonded and typically contain cations of alkali and alkaline earth elements (Na, K, and Ca). Familiar examples are halite (NaCl) (rock salt) and fluorite (CaF₂).

4 - Oxides

The oxide minerals contain various cations (not associated with a polyanion) and oxygen. Examples are hematite (Fe₂O₃) and magnetite (Fe₃O₄).

5 - Hydroxides

These minerals contain the polyanion OH- as the dominant anionic species. Examples include brucite (Mg(OH)₂₎ and gibbsite (Al(OH)₃).

6 - Carbonates

The carbonates contain CO₃^2- as the dominant polyanion in which C⁴⁺ is surrounded by three O^2- anions in a planar triangular arrangement. A familiar example is calcite (CaCO₃). Because NO₃^- shares this geometry, the nitrate minerals such as soda niter (nitratite) (NaNO₃) are included in this group.

7 - Sulfates

These minerals contain SO₄^2- as the major polyanion in which S⁶⁺ is surrounded by four oxygen atoms in a tetrahedron. Note that this group is distinct from sulfides which contain no O. A familiar example is gypsum (CaSO₄ 2H₂O).

 

 

8 - Phosphates

The phosphates contain tetrahedral PO₄^3- groups as the dominant polyanion. A common example is apatite (Ca₅(PO₄)₃(OH)) a principal component of bones and teeth. The other trivalent tetrahedral polyanions, arsenate AsO₄^3-, and vanadate VO₄³- are structurally and chemically similar and are included in this group.

9 - Borates

The borates contain triangular BO₃^3- or tetrahedral BO₄^5-, and commonly both coordinations may occur in the same mineral. A common example is borax, (Na₂B^III₂B^IV₂O₅(OH)₄ 8H₂O).

10 - Silicates

This group of minerals contains SiO₄^4- as the dominant polyanion. In these minerals the Si⁴⁺ cation is always surrounded by 4 oxygens in the form of a tetrahedron. Because Si and O are the most abundant elements in the Earth, this is the largest group of minerals and is divided into subgroups based on the degree of polymerization of the SiO4 tetrahedra.

11 - Orthosilicates

These minerals contain isolated SiO₄^4- polyanionic groups in which the oxygens of the polyanion are bound to one Si atom only, i.e., they are not polymerized. Examples are forsterite (Mg-olivine, Mg₂SiO₄), and pyrope (Mg-garnet, Mg₃Al₂Si₃O₁₂).

12 - Sorosilcates

These minerals contain double silicate tetrahedra in which one of the oxygens is shared with an adjacent tetrahedron, so that the polyanion has formula (Si₂O₇)^6-. An example is epidote (Ca₂Al₂FeO(OH)SiO₄ Si₂O₇), a mineral common in metamorphic rocks.

13 - Cyclosilicates

These minerals contain typically six-membered rings of silicate tetrahedra with formula. (Si₆O₁₇)^10-. An example is tourmaline.

14 - Chain silicates

These minerals contain SiO₄ polyhedra that are polymerized in one direction to form chains. They may be single chains, so that of the four oxygen coordinating the Si atom, two are shared with adjacent tetrahedra to form an infinite chain with formula (SiO₃)^2-. The single chain silicates include the pyroxene and pyroxenoid minerals which are common constituents of igneous rocks. Or they may form double chains with formula (Si₄O₁₁)^8-, as in the amphibole minerals, which are common in metamorphic rocks.

15 - Sheet silicates

These minerals contain SiO 4 polyhedra that are polymerized in two dimensions to form sheets with formula (Si₄O₁₀)^4-. Common examples are the micas in which the cleavage reflects the sheet structure of the mineral.

 

16 - Framework silicates

These minerals contain SiO₄ polyhedra that are polymerized in three dimensions to form a framework with formula (SiO2) 0. Common examples are quartz (SiO₂) and the feldspars (NaAlSi₃O₈) which are the most abundant minerals in the Earth’s crust. In the feldspars Al³⁺ may substitute for Si⁴⁺ in the tetrahedra, and the resulting charge imbalance is compensated by an alkali cation (Na or K) in interstices in the framework.

IGNEOUS ROCKS

 Igneous (Latin, ignis or fire) rocks are formed by cooling and crystallization of molten rocks.

 

Magma

Hot, molten rock material, existing below the earth surface.

Acid Magma:  It is rich in Si, Na and K and poor in Ca, Mg and Fe.

Basic Magma: It is rich in Ca, Mg and Fe and poor in Si, Na and K.

 

Lava

When magma reaches the surface of the earth, it is called lava.

 

Igneous Process

Most igneous process occur underground we can not see them, geologist often rely on geophysical studies of the earths interior, computer models, that simulate subterranean temperature and pressure conditions and laboratory experiment.

 

Melting

A crystalline solid melts when the bonds between its ions break, allowing the charged particles to move freely when under ground temperatures become hight enough bonds in minerals are broken, eventually the heated rock the heated rock no longer a crystalline solid becomes magma, since the various types of  mineral melt at different temperatures, different minerals melt out of the rock as the heat gradually increases hence composition of the magma changes as each newly molten mineral enters and enriches it. Partial melting is described as melting is described as melting points of some but not all of its components minerals, factors control the melting of rocks and creating of magma.

 

1 – Heat = (a-heat produced due to radio active decay of elements, b-form the core of the earth,3-Frictional heat produced as each plate moves.

2 – Pressure = help to increase melting point of a substance.

3 – Water = Water lowers the melting point of substance.

 

Fluidity Of Magma

Its ability to flow, governed by its temperature and composition.

 

Viscosity

Fluids resistance to flow, viscosity increases with decreasing temperature, viscosity increases with silica content.

 

Crystallization

Where temperature decreases bonds start to form and tiny crystals begin to appear. As cooling progress, different minerals crystallize out of the magma at different temperatures.

 

 

 

Classification Of Igneous Rock

 

1 – Texture

2 – Mineral content

 

Texture

It means the size, shape and arrangement of mineral grains

 

Phaneritic

 

1 – State

Metamorphic rocks derived from shale or mudstone a strongly foliated rock known as state, state tends to break parallel to the basic planes into relatively thin, flat fragments, a pattern known as state cleavage.

2 – Phyllite

Low grade metamorphic rock with glossy and shinning lusture, as temperature increase to 300 C, the size of the microscopic mica, chlorite and graphite flakes in state increases, producing the foliated metamorphic rock phyllite.

3 – Schist

When the flakes become visible to the unaided eye, the metamorphic rock is classified as schist, a medium if coarse grain strongly foliated.

4 – Gnesis

It is composed of feldspars, quartz and some mafic minerals, Gneisses are distinguished by minerals that are present in comparatively large amount.

 

Nonfoliated Rocks

 

1 – Marble

When relatively pure limestone and dolostones are metamorphous, even by directed pressure, they tend to form a coarsely granular nonfoliated metamorphic rock marble.

2 – Quartz

A very durable Nonfoliated metamorphic rock come by the metamorphism of quartz sandstone.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Phaneritic

(Form the Greek Phaneros, or visible) When a magma’s minerals crystallize slowly over hundreds or thousands of years, there is ampte time for crystals to grow large enough to be seen by the unaided eye.

 

Aphanitic

(From the Greek a Phaneros, or “not visible”), when magma solidify so quickly that their crystals have little time to grow, and crystals are so small they can barely be seen by the naked eye.

 

Prophyritic

When large crystals are surrounded by small crystals.

 

Glassy

When magma cools so quickly that its ions don’t have enough time to form any crystals, then they are essentially frozen in place, randomly bonded to produce glassy texture.

 

Intrusive OR Plutonic Rocks (for Pluto, the Greek god of the underworld)

Plutonic Rocks are formed when magma cools slowly at great depth with the retention of the volatiles. The texture of such rocks are phaneric.

 

Extrusive OR Volcanic Rocks

Volcanic rocks are formed when the magma erupts at the earths surface and cools rapidly. The volatiles present in the magma escape into the atmosphere. The texture of such rocks is aphanitic or glassy.

 

Hypabyssal Rocks

Hypabyssal Rocks are formed when consolidation of magma takes place very close to the earth’s surface, fine grand with prophyritic texture.

 

Chemical Composition

The earth’s magmas consist largely of the most common elements: oxygen, silicon, aluminum, iron calcium, magnesium, sodium, potassium and sulfur. The relative proportions of these components within a body of magma, added to the prevailing temperature, pressure and its water contents, distinctly characterize magma into following types.

Ultramafic Igneous Rock

Ultramafic Igneous Rocks contain less than 45% silica, here both feldspars and quartz are essentially absent and one or more of the ferromagnesian mineral is the dominant component. These rocks are darker in colors, have a relatively higher specific gravity Gabbro, Dolerite.

 

Intermediate Igneous Rocks

These rock contain silica in between about 55% 65%. They consist of iron and magnesium silicate, along with sodium plagioclase and mica and small amount of quartz. These rocks are lighter in color although a little darker than color of acidic rocks: Example, andesite and diorite.

 

Felsic Igneous Rock

These rocks contain more then 65% silica, these rocks are rich in potassium feldspar, aluminum rich micas and quartz but poor in iron magnesium and calcium silicates. These rocks are light in color and low in specific gravity granite, rhylite.

 

 

Intrusive Rock Formations

Magma moves forcefully into the cracks in preexisting rock, actually pushing the rocks aside to create its own space. I n a similar way, rising magma may force overlying rocks to bulge upward.

 

Mode Of Occurrence

 

Sill

A sill is a sheet like body, lying parallel to layers of preexisting rocks. Sills are produced when intruding magma enters a space between layers of rocks, melting and incorporating adjacent sedimentary material.

 

Phacolith

Magma under low pressure will not exert much pressure to make space for itself, in such cases the magma may be pushed into the existing crests and troughs of a fold in the introduced rocks, and get solidified there. Such structures are in form of crescentric.

 

Laccolith

When thick, viscous magma intrudes between two parallel layers of rock and lifts the overlying rock layers and the form of a dome of arch, it is called Laccolith.

 

Dike

Dike is a vertical wall like igneous body that cuts across preexisting rocks. Dike s are generally steeply inclined or nearly vertical, suggesting that they formed from rising magma, which tend to follow the most direct route upward.

 

Batholith

Batholiths are massive discordant igneous bodies with surface areas of 100 square kilometers or more. They typically form intermediate to high viscosity magmas that, because they flow so slowly, are more likely to remain underground and crystallize here.

 

Lava Flow

Tabular shaped volcanic rock bodies, formed by lava flows.

 

Description Of Common Rocks

 

Granite: It is coarse grained rock which is composed of quartz, alkali feldspar and small amount hornblende. The granites are mostly light in color with a white or pink tint according to the color of the feldspar.

Andesite: These are light colored volcanic rocks. In nature, they are intermediate between acidic and basic rocks. They are general fine grained aphanitic rock with typical prophyritic textures.

Rhyolite: Rhyolite is similar to granite in mineral composition but different texture. The texture is often prophyritic, which contains phenocryst of quartz and feldspar, set in a finely crystalline or glassy groundmass. The color of the rock is generally white, grey or pink.

Obsidian: Obsidian is glassy rock which is acid in composition. It is generally dark colored but show brilliant lusture.

Diorite: It is light colored coarse grained rock of plutonic origin, which is mainly composed of plagioclase feldspar and hornblende. Most diorites contain little or no quartz.

Syenite: It is coarse grained rock light colored rock of plutonic origin, which is mainly composed of orthoclase, soda-plagioclase and or more mafic minerals such as biotite and hornblende.

Gabbro: It is a coarse grained plutonic rock which is dark green or black in color, it is composed of calsic plagioclase, augite and magnetite.

Dolerite: Dolerite is usually dark being almost black when fresh. Its texture is medium to fine grained. It is mainly composed of plagioclase, augite and iron oxide, it is a hypabyssal rock.

Basalt: Basalt is dense looking black volcanic rock. Its texture is fine grained to glassy. It is composed of augit, plagioclase and iron oxide. Sometimes it contains vesicles which have been filled with secondary material.

Peridotite: It is granular, massive, dark colored of plutonic origin, which is composed almost entirely of ferromagnesian minerals like olivine and augit. Quartz and felspars are mostly absent.

Dunite: It is a coarse grained rock which is composed almost entirely of living.

SEDIMENTARY ROCK

When disintegrated products of preexisting rocks are transported and deposited they get lithified forming sedimentary rocks.

 

Weathering

The process by which rocks and minerals break down at or near the earth’s surface.

 

Types Of Weathering  

Physical Weathering: In this type of weathering rocks or minerals break into smaller pieces.

 

Frost Wedging: Water expands in volume by about 9% when it freezes. In case when water enters and freezes into pores or cracks of rock it exerts a great force in surrounding areas. This causes loosening or dislodging fragments of rocks.

 

Crystal Growth: When saltwater enters a crack and evaporates, the growing salt crystals apply great pressure to the walls of the crack which finally tears them apart.

 

Thermal Expansion & Contraction: Rock surface that are exposed to high daytime and low nighttime temperatures their components minerals expands with repeated heating an contract upon cooling, which should eventually cause the rock’s outer layer to break apart.

 

Mechanical Exfoliation: When erosion of overlying rock and soil exposes a wide area of a large plutonic mass, pressure on the mass is reduced and it expands. As the rock in the structure expands, it fractures into sheets parallel to its exposed surface.

 

Chemical Weathering: In this type of weathering changes in chemical composition of minerals or rocks takes place.

 

Dissolution: Process of removal of ion or ion groups by water, layer this water eventually evaporates leaving behind the dissolved substances.   

Oxidations: In oxidation, a mineral’s ion combines with oxygen to form an oxide.

 

Hydrolysis: In hydrolysis, H positive and OH positive ions from water molecules displace other ions from a mineral’s structure, forming a different mineral.

 

Carbonation: The reaction with atmospheric carbon dioxide to form a carbonate.

 

 

 

Products Of Weathering 

Sediments (from Latin sedimentum, meaning “setting”): fragment of solid material.

 

Detrital Sediment: Composed of transported solid fragments.

 

Chemical Sediment: When dissolved minerals either precipitate from solution or are extracted from water by living organisms and converted to sells, skeletons, or other organic substance.

 

Erosion / Transportation

The process by which moving water, wind, ice or gravity carries pieces of rock and deposits them elsewhere.

 

Composition

When transporting media is unable to carry on transporting weathered product, it deposits them at suitable places.

 

Diagenesis

Heat, pressure and the ions alter the physical and chemical nature of both detrital and chemical sediments by a set of processes known collectively as diagenesis.

 

Lithification OR Consolidation:

Lithification (Greek lithos, meaning rock, and latin facere, meaning to make) process of conversion of loose sediment into solid sedimentary rock.

 

1 – Compaction & Dehydration

The process by which pressure reduces the volume of sediments by squeezing out excess water which increased the cohesion of sediments.

 

2 – Cementation

Material originally dissolved during chemical weathering precipitate from water circulating through sediment, creating a chemical cement that binds the sediment grains together.

 

Sediment Texture 

Grain Size: Different rocks produce grains of different size, shapes and resistance to weathering.

 

Grain Shape: The more vigorous collision a particle experiences and the father it moves away from its parent rock, the more rounded it becomes.

 

Sorting: The process by which a transport medium selects particles of different sizes, shapes or densities.

 

Sedimentary Structure

Physical features that reveal the conditions under which sediment deposition occurred.

 

1 – Stratification

The deposition of sediments into layers or beds is called stratification.

 

2 – Lamination

Thin bedding, less than one centimeter in thickness are called lamination.

 

3 – Grade Bedding

During deposition when particles settle at different rates, depending on their sizes, densities and shapes, they produce beds of coarse particles at bottom and fine particles at top.

 

4 – Cross Bedding

It is consist of sedimentary layers deposited at an angle to the underlying set of beds.

 

5 – Ripple Marks

Ripple marks are the symmetrical or unsymmetrical undulations which may be seen on the surface of some sedimentary deposit. Produced by waves and currents in shallow water.

 

Classification Of Sedimentary Rocks

On the basis of mode of origin.

 

1 – Detrital / Clastic Sedimentary RockRocks that consists of preexisting solid particles compacted and cemented together, depending upon the particles size they are:  

Mudstone: Rocks with grain size less than 1/256 mm to diameter lacking any fissilty in their structure.

Shale: Rock with grain size less than 1/256 mm in diameter with fissile structure, which is their ability to split into very thin parallel surfaces.

Siltstone: Detrital sedimentary rock with grain size ranging from 1/256-1/16 mm in diameter.

Sandstone: Detrital sedimentary rocks with grain size range from 1/16 mm to 2 mm in diameter.

Conglomerate: Detrital sedimentary rock with grain size larger than 2 mm in diameter, the larger grains are rounded and embedded in fine grained ground mass.

Breccia: Detrital sedimentary rock with grain size larger than 2 mm in diameter, the larger grains are angular and embedded in fine grained matrix.

 

2 – Chemical Sedimentary Rock

Rock formed when dissolved minerals either precipitate or evaporated from solution.

 

Limestone: Composed largely of calcium carbonate, forms by the process of precipitation.

Evaporite (Rock Salt, Gypsum): Formed when salty water evaporates.

Chert: Consist largely of silicate, formed by the process of precipitation.

 

Organic Sedimentary Rock

Formed by accumulation of plant remains.

Calcareous Rock

Limestone

Coal Steam