13 Mineralogy- Minerals, types

Rachna Bhateria

Objectives

 

To study about Mineralogy and Minerals in general To discuss the physical properties of Minerals To discuss the classification of minerals

 

Introduction

 

Different geological processes are responsible for the concentration of minerals in the parts of crust. Quartz contributes about 70 % of the continental crust and is the most common mineral. Minerals which contain both silicon and oxygen are known as silicates. Oxygen and silicon can be joined together in different ways to form silicate structures like feldspar and augite, olivine, etc. (Figure 1). About 96 percent of the minerals found in Earth’s crust are silicates. There are over 100 elements known presently but over 99% of the Earth’s crust is composed of just 8 elements i.e. oxygen (O), silicon(Si), aluminium (Al), iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K). About 4000 plus minerals have been so far discovered. Out of which only a few hundred are considered to be common. An economic concentration or reserves of metallic minerals in a rock is known as ore. Noneconomic minerals like quartz, feldspar and calcite which are found in association with ore minerals are known as gangue (pronounced “gang”) and are considered waste. It is insufficient to form an ore from average concentration of minerals in the crust.

16.1 Mineralogy

 

Mineralogy is the branch of science which deals with the physico-chemical study of naturally occurring solid and crystalline materials. We can also say that it is the scientific study of all aspects of minerals concerning with conditions of formation during their origin and natural distribution. Internal structure of crystal, physical properties and chemical composition of minerals all are included in mineralogy.

A mineral is a homogeneous naturally occurring solid substance formed by inorganic processes having a definite but not fixed chemical composition with an ordered atomic arrangement.

 

 

16.2 Chemical Composition of Minerals

 

Elements are the building blocks of minerals. Geochemical factors such as element abundance, solid solution limits, mineral stability, place a limit on the composition and stability of naturally occurring compounds, hence, there are relatively less number of minerals. Minerals and synthetic compounds may have identical structures. However, they differ in the fact that minerals are rarely pure substances and typically show wide variation in their composition. According to the composition, variation of minerals ranges from pure elements (Fe, Au, Ag) with relatively simple compounds (eg. PbS galena, KCI- sylvite) to very complex compounds (eg. Steenstrupine). Chemically simple minerals (SiO2) do not necessarily have simple structures, e.g., alpha quartz. Chemical classifications of minerals are based on the predominant anion or anionic group. The following classes are recognized: (1) native elements; (2) sulphide, telluride, arsenide and selenide minerals including sulphosalts of antimony and bismuth; (3) halides; (4) oxides; (5) hydroxides; (6) carbonates; (7) nitrates; (8) borates; (9) chromates; (10) tungstates; (11) molybdates; (12) phosphates; (13) arsenates; (14) vanadates; (15) silicates and aluminosilicates. Because of the dominance of oxygen, silicon and aluminum in the earth, silicates and aluminosilicates are quantitatively the most important class of minerals. Minerals of mixed anion composition, e.g. F in topaz or apatite, S in pyrite, OH in talc and mica, Cl in biotite, are usually classified according to the nature of the dominant anion. Hybrid minerals, such as valleriite and tochilinite, are sulphides containing layers of hydroxides, and are not common. Each major  compositional class of minerals is subdivided into groups of minerals having similar crystal structures (Table 1).

16.3 Structural Classification of Silicates

 

The silicate and alumino silicate class comprise orthosilicates, sorosilicates, inosilicates, phyllosilicates and tectosilicates, etc. Each of these divisions is further subdivided into mineral groups of different structure, e.g. the cyclosilicates into, beryl, tourmaline and axinite groups. The divisions arise because atoms of similar size and bonding character adopt similar structures with a particular anion or anionic group. Hence, minerals of very different composition possess the same crystal structure. Silicates are compounds where Si and O are abundant and are major mineral components of the earth’s crust and mantle’. The basic unit for all silicates is the (SiO4)4-tetrahedron (Figure 2). Variety of silicate minerals are produced by the (SiO4)4- tetrahedra linking to self-similar units sharing one, two, three, or all four corner oxygens of the tetrahedron. Silica minerals are classified based on how the silica tetrahedral are linked.

Tetrahedra may be isolated or be linked in rings, single chains, double chains, sheets, or frameworks. Let us discuss:

(1) Nesosilicates (Independent/Isolated tetrahedral group) [(SiO4)4- ]:

When the isolated tetrahedra are linked by the bonding of each oxygen ion of the tetrahedron to a cation, the cation in turn bond to the oxygen of other tetrahedral (Figure 3a). Thus the tetrahedra are isolated from one another by cations on all sides. The ratio of oxygen to silica is 4:1. Examples of such silicate minerals are olivine, garnet, zircon, etc.

 

(2) Sorosilicates (Double Tetrahedral group) [(Si2O7)6-]:

In this type two tetrahedra are linked by a single oxygen atom or in other words, two tetrahedra share one oxygen (Fig. 3b). The ratio of oxygen to silica is 2:7 or 3.5:1 (Figure 3b). Example of this type of silicate structure is epidote, melilite.

 

(3) Cyclosilicates (Ring structure) [(Si6O18)12-] or [(Si3O9)6-]:

When angular position of tetrahedra is such that it forms a ring. Closed rings of tetrahedral each sharing 2 oxygen ((Figure 3c). The ratio of oxygen to silica is 3:1. It forms following three types of closed rings:

 

(i)     each of 3 tetrahedra sharing an oxygen ion such as in mineral benitoite

(ii)   each of 4 tetrahedra sharing an oxygen ion such as in mineral axinite (iii)each of 6 tetrahedra sharing an oxygen ion such as in mineral beryl.

  • (4) Inosilicates

 

(a) Single Chain (SiO3)2-:

 

Single chains also form by sharing oxygen but in this case, two oxygens of each tetrahedron bond to adjacent tetrahedra but in an open-ended chain instead of a closed ring. Single chains are linked to other chains by cations (Figure 4a). The ratio of oxygen to silica is 3:1. Example of such silicates are the pyroxene group of minerals.

(b) Double Chain (Si4O11)6- :

These are continuous double chains of tetrahedral alternatively sharing two and three oxygen. In this case, two single chains combine to form double chains linked to each other by shared oxygens. Adjacent double chains linked by cations form the structure of the amphibole group of minerals (Figure 4b). A common mineral, hornblende has a complex composition including calcium, sodium, magnesium, iron and aluminium. The ratio of oxygen to silica is 2.75:1.

5) Phyllosilicates (sheet silicates) [(Si2O5)2-]:

 

Sheets are structures in which each tetrahedron shares three of its oxygens with adjacent tetrahedra to build stacked sheets of tetrahedra. Cations may be interlayered with tetrahedra sheets (Figure 5a). The ratio of oxygen to silica is 2.5:1. The micas and clay minerals are the most abundant sheet silicates. The minerals with sheet structures can be separated into extremely thin sheets.

(6) Tectosilicates (3-D Framework) [(SiO2)0]:

Three dimensional framework form when each tetrahedron shares all its oxygens with other tetrahedra (Figure 5b). In this silicate structure, the ratio of oxygen to silica is 2:1. Minerals of feldspars and quartz are the examples of this type of silicate structure.

 

Figure 5: Crystal structure of (a) phyllosilicate minerals and (b) tectosilicate minerals.

 

16.4 Physical Properties of Mineral

 

The mineral can often be identified in the field using basic following properties (figure 6):

 

  • Color
  •  Streak
  •  Hardness
  •  Cleavage or fracture
  • Crystalline structure
  • Diaphaneity or amount of Transparency
  • Tenacity
  • Magnetism
  • Lustre
  • Odour
  • Taste and
  • Specific Gravity

1. Colour

 

 

Idiochromatic minerals are said to be “self coloured” minerals because of their composition. The color of these minerals is caused by the presence of element(s) in the chemical composition of the mineral. e. g. Cu in azurite (blue), Cu in malachite (green), Mn in rhodonite and rhodochrosite (pink).

 

 

Allochromatic minerals are said to be “other colored” as impurities in traces are present in their composition or due to defects in their structure. In these minerals, the color is a variable and unpredictable property. e. g. blue in Amazonite (orthoclase), yellow in Heliodor (spodumene) and the rose in rose quartz.

Pseudochromatic minerals are “false colored” due to tricks in light diffraction. In these cases, color is variable but a unique property of the mineral. Examples are the colors produced by precious opal and the shiller reflections of labradorite.

 

Play of colors

 

One of the salient features of color mechanisms is the play-of-colors. Interference of light reflected from the surface or from within a mineral may cause the color of the mineral to change as the angle of incident light changes. This gives the mineral a beautiful iridescent quality and colors to the minerals for example, bornite (Cu5FeS4), hematite (Fe2O3), sphalerite (ZnS), opal and some specimens of labradorite (plagioclase). It is sometimes seen on tarnished sulfides like chalcopyrite or pyrite and occasionally on an oxide or a silicate mineral. It is caused by an optical effect called interference. When light strikes a shiny, transparent layer at an oblique angle the light rays are split – part of the light is reflected off the upper surface and part goes into the layer. Some of the light that enters the layer is reflected off the bottom surface and exists parallel to the other reflection. However, white light is composed of a numbers of colors, each of which travels at a different speed in the layer. So when the split light rays emerge from the layer they have been retarded and their wave patterns are out of synchronization with the part of the light reflected off the top of the layer. One or two colors will be in phase and the rest out of phase. The in phase color will be very bright and the out of phase colors will be very pale or absent. Thus, we may see a rich, glowing color coming from a colorless, transparent stone, but only in one special direction.

 

Colours due to wavelength of light

 

Minerals are colored because certain wavelengths of light are absorbed, and the mineral color then results from the combination of those wavelengths which reach the eye if light is

not absorbed, the mineral is colorless in reflected or refracted light and is black if all wave- of light are absorbed. Pleochroism may be present in certain minerals if light travels along crystallographic axes. A mineral may display more than one color when rotated or viewed at different angles. Cordierite specimens often display a clear-white and violet color when rotated indicating a dichroism quality.

 

Colour due to impurities

 

Tiny amounts as little as one tenth of 1% of an impurity in the molecular structure of a mineral can determine that mineral’s color. The amount and type of impurities affects the color of the mineral. Minerals with an inherent color have essential elements in them which cause their color. The examples are Azurite and Malachite, which have their strong blue and green color due to their copper in their atomic structure. But there are many minerals which have slight additions of color-causing elements in some specimens that cause it to be a different color. For example, pure Quartz (SiO2), is colorless, whereas Amethyst, a purple variety of quartz, has its purple color caused by traces of the element iron. The amount of iron present determines the intensity of the color. Trace amounts of titanium or manganese turn quartz pink.

 

Colour due to charge transfer

 

When two or more elements in a mineral exchange electrons then this is called charge transfer. The movement of electrons results in selective absorption of light. For Example,

 

Sapphire: Sapphires contain small amounts of titanium and iron. The electron transfer between Ti and Fe causes light in the yellow through red spectrum to be absorbed, producing the deep blue color sapphires.

 

Aquamarine: Small amounts of iron in valence states Fe2+ and Fe3+ cause an electron transfer that absorbs red light, resulting in the color blue.

Tourmaline: When manganese (Mn2+) and titanium (Ti4+) swap electrons, it creates a yellow-green color.

 

2. Streak

 

Streak is the color of the mineral in powdered form. The streak of a mineral is quite different than the mineral. Although the colour of a mineral may vary, the streak is usually constant and is thus useful in mineral identification. Streak is a more accurate illustration of the mineral’s color, streak is a more reliable property of minerals than color for identification.

 

3.      Hardness

 

Friedrich Mohs in 1812 developed a standard scale for calculating the extent of hardness. Hardness varies greatly in minerals. Its determination is one of the most important tests used in identification of minerals. Hardness is the resistance offered by smooth surface of a mineral on scratching. The hardness of a mineral might be said to be its “scratchability”. Hardness, like many other physical properties depends upon atomic structure of mineral. It varies with density of packing in structure. On the basis of their relative hardness, minerals are ranked from 1 to 10. Softer minerals are scratched by harder minerals. Moh’s scale is based on the ten index minerals while other minerals are ranked relative to these. For instance, a mineral having hardness of 6.5 can scratch feldspar but not quartz.

 

 

Moh’s Hardness Scale

 

Talc                     Soft

 

Gypsum

 

Calcite

 

Fluorite

 

Apatite

 

Feldspar

 

Quartz

 

Topaz

 

Corundum

 

Diamond        Hardest

 

 

4. Cleavage

 

In most of the crystals, strength of bonding in all directions is not equal which will be liable to crack along crystallographic directions representing a fracture property by reflecting the

 

 

fundamental structure which can be analytical. Regular flat faces which resemble growth faces like in calcite and mica are the results of perfect cleavage. Cleavage is the property of a mineral to break along planes where bond strength is low in the chemical bond. A cleavage is said to be imperfect or parting when it is less developed. Parallel sheets are produced when some minerals break along one dominant plane of cleavage while prism or blocks results from breakage along two or more planes (Table 2).

Fracture

 

Fracture describes the quality of the cleavage surface. Most minerals display either uneven or grainy fracture, conchoidal (curved, shell-like lines) fracture, or hackly (rough, jagged) fracture.

 

If the mineral contains no planes of weakness, it will break along random directions called fracture. Following kinds of fracture patterns are observed:

Conchoidal fracture – breaks along smooth curved surfaces. Fibrous and splintery – similar to the way wood breaks.

Hackly – jagged fractures with sharp edges.

Uneven or Irregular – rough irregular surfaces.

 

Parting

 

Parting is also a plane of weakness in the crystal structure, but it is along planes that are weakened by some applied force. It therefore may not be apparent in all specimens of the same mineral, but may appear if the mineral has been subjected to the right stress conditions.

 

5.    Crystal form

 

Crystal form is the external expression of the internal ordered arrangement of atoms. During mineral formation, individual crystals develop well-formed crystal faces that are specific to that mineral. They reflect the internal symmetry of the crystal structure that makes the mineral unique. 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. The crystal faces for a particular mineral are characterized by a symmetrical relationship to one another that is manifest in the physical shape of the mineral’s crystalline form. Crystal forms are commonly classified using six different crystal systems (Figure 7 (a-f)), under which all minerals are grouped.

The six major crystal forms are given below:

(a)   Cubic or Isometric the simple cubic system has one lattice point on each corner of the cube with each lattice point shared equally between eight adjacent cubes. eg. Halite as rock salt


  • (b) Tetragonal crystal lattices result from stretching a cubic lattice along one lattice vectors, making the cube a rectangular prism with a square base.         e g. Zircon..
  • (c) Orthorhombic lattices are made by stretching a cubic lattice along two lattice vectors by two factors, forming a rectangular prism with a rectangular base. All three bases intersect at 90 degree angles and the three lattice vectors are mutually orthogonal. e g. Aragonite
  • (d) Hexagonal lattice has the same symmetry as a right prism with a hexagonal base. Graphite is an example of a hexagonal crystal.
  • (e) Monoclinic lattice is described by vectors of unequal length that form a rectangular prism with a parallelogram as base. Two pairs of vectors are perpendicular, while the third pair makes an angle other than 90 degrees. e g. Orthoclase
  • (f) Triclinic crystal is described by vectors of unequal length. All three vectors are not mutually e g. Copper sulphate
  1. Tenacity

 

Tenacity is the tendency of a mineral to deform plastically under stress. Minerals may be brittle and can be fractured under stress such as silicates and oxides. Minerals can be sectile as they can be cut with a knife or they can be ductile by deforming readily under stress as does gold. The following chart below gives the list of terms used to describe tenacity and a description of each (Table 3).

 

7. Luster or transparency

 

Luster refers to the general appearance of a mineral surface in reflected light. Mineral luster can be metallic or non-metallic. The mineral is metallic when it is opaque and reflects like metals. Minerals with metallic luster are usually opaque and have a colored streak .Non-metallic luster can be :

 

1.      vitreous eg. Quartz, calcite

2.      resinous eg. Sulfur

3.        pearly eg. Barite

4.      greasy eg. Calcite

5.        silky eg. Asbestos

6.        Adamantine eg. Feldspar

 

Alternatively, it is non-metallic when mineral does not reflect light. When the mineral looks like paraffin or wax then it is said to be waxy. Examples include jade and chalcedony . The mineral is vitreous when it looks like broken glass and it is pearly when appears iridescent for example muscovite and stilbite. The mineral looks fibrous like silk then it is termed as silky. Examples of silky minerals include asbestos, ulexite and the satin spar variety of gypsum. Themineral is greasy when looks like oil on water. Resinous minerals looks like hardened tree sap (resin), example is amber. Admantine looks brilliant, like diamond. Greasy minerals resemble fat or grease. A greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions for example opal and cordierite.

  1. Specific gravity

 

Specific gravity is a definite physical property calculated in g/cm3. It can be calculated by the measurement of volume with displacement of water in a graduated cylinder and the mass. Specific gravity is a dimensionless quantity. Different minerals have different Specific gravity e.g. Iron (8), lead (13) and gold (19). The range of specific gravity is from 2.6-3.5 for silicates and from 5-6 for sulfides. Mineral with various specific gravity are summarized in Table 4. Specific gravity (SG) is calculated by the determination of the weight in air (Wa) and the weight in water (Ww) and specific gravity can be calculated using following formula:

 

SG = Wa / (Wa-Ww).

 

Table 4: Mineral with various Specific gravity

 

16.5 Geological processes of Minerals Formation

 

  1. Magmatic deposits

 

Magmatic deposits result from simple crystallization and concentration by differentiation of intrusive igneous masses. They have high melting points so that they can co-exist and get crystallized from silicate melts at temperatures above 800º C. Granites, granodiorites, and rhyolites, along with rich minerals like quartz, muscovite and alkali feldspars are Felsic igneous rocks. These minerals are usually light in color and the color is not always diagnostic. Pegmatite (PEG) is a third mineral environment showing concluding stages of fractionation in igneous rocks. It is very coarse grained and similar to silicic igneous rock in composition with high silica. There are certain elements which readily do not substitute in abundant minerals and are termed as incompatible elements. In pegmatites, they made their own minerals by accumulation. Minerals containing the incompatible elements, Li, Be, B, P, Rb, Sr, Y, Nb, rare earths, Cs, and Ta are typical and characteristic of pegmatites (Deer et al., 1962, 1974, 1980). Rocks composed mostly of pyroxene, calcium-rich plagioclase, and minor amounts of olivine make up the mafic family of igneous rocks. The mafic magmas are somewhat more viscous than the ultramafic magmas, but they are still fairly fluid.The low silica and gas contents make ultramafic very fluid; i.e., they have a low viscosity, or resistance to flow. Ultramafic rocks are given names depending on whether they are intrusive or extrusive. Peridotite is the name given to intrusive ultramafic rocks, whereas komatiite is the name given to extrusive ultramafic rocks. Peridotite and komatiite are compositionally identical. Their textures, however, are different reflecting their mode of formation. Peridotite appears to be the dominant rock type of the upper mantle.

 

  1. Sedimentary mineral deposits

 

The formation of sedimentary rocks is accompanied by three processes. The first process is the weathering which produces the materials that a sedimentary rock is composed of by mechanical (freezing, thawing) and chemical (dissolution of minerals, formation of new minerals [clays]) interaction between atmosphere, hydrosphere and earth surface rocks. The second process is the transport which moves these materials to their final destination.

 

 

 

Rivers are the main transporting agent of material to the oceans (glaciers are at times important). During transport the sediment particles will be sorted according to size and density (gold placers) and will be rounded by abrasion. Material that has been dissolved during weathering will be carried away in solution. Winds may also play a role (Sahara — east/central Atlantic). The sorting during transport is important because it is the reason that we have distinct clastic rock types (conglomerates, sandstones, shales). The third process is the deposition of sediment which occurs at a site with a specific combination of physical, chemical and biological conditions i.e. the sedimentary environment.

  1. Metamorphic rock mineral

 

Metamorphic processes occur to make adjustments between the chemical potential of any system and the changes in temperature and pressure. Metamorphism involves both chemical and mechanical changes but in varying proportions. Metamorphic minerals and rocks provide many valuable resources, marble and slate the two most widely used. Metamorphic rocks are formed when the precursor materials (igneous, sediment, etc.) are buried deeply and are consequently brought into an environment of high pressure and temperature. Therefore, they are most commonly encountered in the core zones of mountain belts (uplifted root zone), in old continental shields, and as the basement rock below the sediment veneer of stable continental platforms. Metamorphic rocks and associated igneous intrusions (from rock buried so deep that it melted) make up about 85% of the continental crust. Metamorphic rocks may contain relic structures, such as stratification, bedding, and even such features as sedimentary structures or volcanic textures.

 

  1. Hydrothermal mineral deposits

 

Hydrothermal mineral deposit is the fourth major mineral environments. The elements it contains and the minerals formed by this process are very different from regional and contact metamorphic rocks therefore; it becomes inevitable to consider them as isolated group. With increase in depth, there is a scarcity of water so minerals in the form of magma  approach to the earth’s surface through crust. Woods Hole Oceanographic Institute (USA) explored the floor of ocean with the use of submersible craft and discovered the hot waters plumes which were coming out along the oceanic ridge. The plumes of hot water contain manganese, copper, iron and zinc which are dissolved sulfide metals and the mineral deposits produced by them were termed massive sulfides. When viewed in the lights of submersible craft the water coming from tall hydrothermal vent resembled the smoke coming from chimney due to precipitated minerals and the vents were named as “black smokers”. These may be sub-classified as high temperature hydrothermal (HTH), low temperature hydrothermal (LTH), and oxidized hydrothermal (OXH). Sulphide minerals generally consist of minerals which are present centrally and on the right hand side in the periodic table (e.g. Cu, Ag, As, Sb Sn, Pb, Zn, Hg, Cd) and are generally known as chalcophile elements. Sulfides are mostly hydrothermal but they may occur in metamorphic and igneous rocks. Silver, tungstate minerals, the tellurides chalcopyrite, gold, bornite, and molybdenite are all high temperature hydrothermal minerals and the hydrothermal minerals with low temperature include pyrite, barite, cinnabar, gold, and cassiterite. Sulfide minerals will weather by oxidation to form oxides of the sulfates and carbonates of the chalcophile metals as they are not stable in atmospheric oxygen. These types of mineral are the feature of oxidized hydrothermal deposits and are known as gossans. They show characterized mark i.e. red- yellow stains of iron oxide on the surface of rock. They generally separate mineralized zones at depth and are very common in Colorado.

16.6 Mineral Classification

 

Minerals can be arranged and classified (figure 8) on the basis of their chemical composition and internal crystal structure.

Based on chemical classification, there are 7 major mineral groups which are given below:

 

  1. Silicates
  2. Native Elements
  3. Halides
  4. Carbonates
  5. Oxides
  6. Sulfates
  7. Sulfides

 

Silicates

 

Silicates are the most abundant minerals in Earth’s crust and are composed of oxygen and silicon elements in combinations with the cations of other elements.

Silicate minerals are most important rock-forming minerals and are regarded as building blocks of the common rock-forming minerals. According to an estimate, about 27% of all known minerals and about 40% of common rock forming minerals are silicates. Silicate minerals make up ~90% of rocks in the Earth’s crust.

 

The common rock- forming silicates minerals are listed here:

 

Olivine Garnet

 

Pyroxenes Amphiboles Micas

 

Feldspars

 

Feldspathoids and Silica group

 

Among all the minerals, plagioclase feldspar is the most abundant minerals in the earth.

 

 

Native elements

 

Native elements are the minerals which consist of a single element.

Examples are: gold (Au), silver (Ag), copper (Cu), iron (Fe), diamonds (C), graphite (C), and platinum (Pt).

 

Halides

 

Halides consist of halogen elements, chlorine (Cl), bromine (Br), fluorine (F), and iodine (I) forming strong ionic bonds with alkali and alkali earth elements such as sodium (Na), calcium (Ca) and potassium (K).

Examples include halite (NaCl) and flourite (CaF2)

Carbonates

 

Carbonates are anionic groups of carbon and oxygen. Carbonate minerals result from bonds between these complexes and alkali earth and some transitional metals.

Common carbonate minerals include calcite CaCO3, calcium carbonate, and dolomite CaMg(CO3)2 , calcium/magnesium carbonate.

Oxides

 

Oxides are minerals that include one or more metal cations bonded to oxygen or hydroxyl anions.

Examples are hematite (Fe2O3), magnetite (Fe3O4), corundum (Al2O3), and ice (H2O)).

 

Sulfates

 

Sulfates are minerals that include SO4 anionic groups combined with alkali earth and metal cations.

Anhydrous (no water) and hydrous (water) are the two major groups of sulfates.

Barite (BaSO4) is an example of a anhydrous sulfate and gypsum (CaSO4 · 2H2O) is an example of a sulfate.

 

Sulfides

 

Sulfides are minerals composed of one or more metal cations combined with sulfur. Many sulfides are economically important ores.

Pyrite  (FeS2)  or  “fool’s  gold”,  galena  (PbS),  cinnabar  (HgS)  and  molybdenite

(MoS2) are a few commonly occurring sulfide mineral.

 

 

16.7 Uses of minerals

 

Industrial uses

 

Calcite is mined primarily to make cement, be used as a flux in the smelting of metallic ores, be used as a fertilizer, or used as a building stone or construction material.

 

Limestone is used as crushed stone in road construction and other construction; for ballast in railcars; for the manufacture of cement; as a filter; to absorb SO2 emissions at coal plants; to adjust pH in soil; and in animal feeds.

Garnet is ground to a variety of sizes to be used as an abrasive. Garnet is also used in sandpaper, sanding belts, discs, and strips.

 

Gypsum is used in wallboard and plaster products. It is also used to make Portland cement and has some agricultural applications. A small amount of very pure gypsum is used in glass making.

Hematite is a common ore of iron because it contains about 70% iron. Once mined, the iron from the hematite is then mixed with other elements in order to make it into steel, the most common use of iron ore.

 

 

Abrasives

 

Quartz sand is hard enough for woodworking.

 

Corundum is the workhorse abrasive of sandpaper. Extremely hard (Mohs 9) and sharp, corundum is also usefully brittle, breaking into sharp fragments that keep on cutting. It’s great for wood, metal, paint and plastic. All sanding products today use artificial corundum — aluminum oxide.

Diamond paste is available in many grades for sharpening hand tools, and you can even buy nail files impregnated with diamond grit for the ultimate grooming aid. Diamond is best suited for cutting and grinding tools, however, and the drilling industry uses lots of diamond for drill bits.

 

Ceramic

 

The important geological sources for silica suitable for the ceramic industry are the pegmatites (with well-developed crystals of quartz), vein quartz, and sandstones of high siliceous nature, high silica sands and orthoquartzites.

Feldspars are used as fluxing material in the preparation of ceramic bodies, enamels and glazes. Commonly potash feldspars (orthoclase and microcline) are used for this purpose and soda feldspar is chiefly used for glazing purposes.

 

Electrical

 

Coltan is a metallic ore composed of niobium and tantalum. Coltan is refined into metallic tantalum, which with its unique capacitor properties is then used in computers, cell phones, video game consoles, GPS, video cameras, and other micro-electrical circuits.

Gold has many practical uses in electronics. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring.

 

Summary:

 

We studied about the composition, internal structure and properties of minerals We studied about the mineral deposits found in the environment including igneous, metamorphic and sedimentary mineral deposits We studied the classification and uses of minerals.

 

References