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KAFEREL-SHEIKHUNIVERSITY

SCIENCECOLLEGE
GEOLOGIC DEPARTME NT


MINERALOGY




BY
NAHED HUSSEIN EL-SHIBINY


















1

INTRODUCTION

Mineralogy is the study of naturally occurring, crystalline substances-minerals. Everyone has a certain familiarity with minerals for they are present in the rocks of the mountains, the sand of the sea beach, and the soil of the garden. Less familiar, but also composed of minerals are meteorites and the lunar surface material. A knowledge of what minerals are, how they were formed, and where they occur is basic to an understanding of the materials largely responsible for our present technologic culture. For all inorganic articles of commerce, if not mineral themselves, are mineral in origin.


DEFINITION OF 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.

The qualification naturally occurring distinguishes between substances formed by natural processes and those made in the laboratory.
The definition further states that a mineral is a homogeneous solid. This means that it consists of a single, solid substance that cannot be physically subdivided into simpler chemical compounds.
The qualification solid excludes gases and liquids. Thus H2O as ice in a glacier is a mineral, but water is not. However, in a classification of natural materials such as substances that otherwise are like minerals in chemistry and occurrence are called mineraloids.
The statement that a mineral has a definite chemical composition implies it can be expresses by a specific chemical formula. For example, the chemical composition of quartz is expresses as SiO2. Because quartz contains no chemical elements other than silicon and oxygen, its formula
is definite. Most minerals, however, do not have such well-defined compositions. Dolomite, CaMg(CO3) 2, is not always a pure Ca-Mg-carbonate. It may contain considerable amounts of Fe and Mn in place of Mg.
An ordered atomic arrangement indicates an internal structure framework of atoms (or ions) arranged in a regular geometric pattern. Sine this is the criterion of a crystalline solid, minerals are crystalline. Solids, such as glass, that lack an ordered atomic arrangement are called amorphous. Several natural solids are amorphous.
According to the traditional definition, a mineral is formed by inorganic processes. We prefer to preface this statement with usually and thus include in the realm of mineralogy the few organically produced compounds that answer all the other requirements of a mineral. The outstanding example is the calcium carbonate of mollusk shells. Other examples are elemental sulfur formed by bacterial action and iron oxide precipitated by iron bacteria. But petroleum and coal, frequently referred to as mineral fuels, are neither a definite chemical composition nor an ordered atomic arrangement. However, in places coal beds have subjected to high temperature which have driven off the volatile hydrocarbons and crystallized the remaining carbon. This residue is the mineral, graphite.
In nature minerals are extremely widespread. The whole of the Earth's crust, all rocks and deposits consist of minerals.
Mineral individuals range in size from large crystals, whose mass is several tons (feldspar, quartz),to minute grains observable only under the microscope. Most minerals in fact occur in small and minute grains and form the granular texture of igneous, sedimentary and metamorphic rocks.



ECONOMIC IMPORTANCE OF MINERALS
Since before historic time, minerals have played a major role in humanity’s way of life and standard of living. With each successive century they have become increasingly important, and today we depend on them in countless ways, from the construction of skyscrapers to the manufacture of televisions. Modern civilization depends on and necessitates the prodigious use of minerals. A few minerals such as talc, asbestose, and sulfur are used essentially as they come from the ground,
but most are first processes to obtain a useable material. Some of the more familiar of these products are: bricks, glass, cement, plaster, and a score of metals ranging from iron to gold. Metallic ores and industrial minerals are mined on every continent wherever specific minerals are sufficiently concentrated to be economically extracted.
The location of mineable metal and industrial mineral deposits, and the study of the origin, size, and ore grade of these deposits is the domain of economic geologists. But a knowledge of the chemistry, occurrence, and physical properties of minerals is basic to pursuits in economic geology.
NAMING OF MINERALS
Minerals are most commonly classified on the basis of the presence of a major chemical component into oxides, sulfides, silicates, carbonates, phosphates, and so forth. This is especially convenient because most minerals contain only one major anion..
The careful description and identification ofminerals often requires highly specialized techniques such as chemical analysis and measurement of physical properties, among which are the specific gravity, optical properties, and X-ray parameters which relate to the atomic structure of minerals. Minerals may be given names on the basis of some physical property or chemical aspect, or they may be named after a locality, a public figure, a mineralogist, or almost any other subject considered appropriate. Some examples of minerals names and their derivations are as follows:
Albite (NaAlSi3O8) from the Latin, albus (white),in allusion to its color.
Chromite (FeCr2O4) because of the presence of large amount of chromium in the mineral.
Magnetite(Fe3O4) because of its magnetic properties.
Sillimanite(Al2SiO5) after Professor Benjamin Silliman of Yale University (1779-1864).
Franklinite(ZnFe2O4) after a locality, Franklin, New Jersy, where it occurs as the dominant zinc mineral.
An international committee, the Commission on New Minerals and New Minerals Names of the International Mineralogical Association, now reviews all new mineral descriptions and judges the appropriateness of new mineral names as well as the scientific characterization of newly discovered mineral species.
Minerals associations
There are definite associations between specific minerals and certain kinds of rocks. Following are some examples:
a)platinum: associates with norites, peridotites and their alteration products.
b)Chromite : associates with peridotites, anorthite and similar rocks.
c)Titaniferous magnetite and ilmenite: associate with gabbros and anorthites.
d)Magnetite: occurs with syenite
e)Nickel-copper: with norites
f)Corundum: with nepheline syenite
g)Diamound: in kimberlite (a variety of peridotite)





2
PHYSICAL PROPERTIES OF MINERALS
In this chapter we examine those physical properties that can be determined by inspection or by relatively simple tests. Because they are determined in hand specimens, they are important in the rapid recognition of minerals. Other physical properties, such as those determined by X-ray or optical techniques, require special and often sophisticated equipment and may involve elaborate sample preparation.

CRYSTAL HABITS AND AGGREGATES
The habit or appearance of single crystals as well as the manner in which crystals grow together in aggregates are of considerable aid in mineral recognition. Terms used to express habit and state of aggregation are given below.
1-Minerals in isolated or distinct crystals may be described as:
a) Acicular. Slender, needlike crystals.
b) Capillary and filiform. Hairlike or thread-like crystals.
c) Bladed. Elongated crystals flattened like a knife blade.
2-For groups of distinct crystals the following terms are used:
a)Dendritic. Arborescent, in slender divergent branches, somewhat plantlike.
b)Reticulated. Latticelike groups of slender crystals.
c)Drusy. A surface covered with a layer of small crystal
d) Divergent or radiated. Radiating crystal groups.
3-Parallel or radiating groups of individual crystals, are described as:
a)Columnar.Coumnlike individuals.
b)Bladed. An Aggregates of many flattened blades
c)Fibrous. Aggregates of slender fibers, parallel or radiating.
d)Globular. Radiating individuals forming small spherical or hemispherical groups.
e)Reniform. Radiating individuals termination round kidney-shaped masses.
f)Mammillary. Large rounded masses resmbling mammae, formed by radiating individuals
g)Colloform. Spherical forms composed of radiating individuals without regard to size; this includes reniform and mammillary.
4-A mineral aggregates composed of scales or lamellae is described as:
a)Foliated. Easily separable into plates or leaves.
b)Micaceous. Similar to foliated, but splits into exceedingly thin sheets, as in the micas.
c)Lamellar or tabular. Flat, platelike individuals.
d)Plumose. Fine scales with divergent or feathlike structure.
5-A mineral aggregates composed of grains is grainular.
6-Miscellaneous terms:
a) Concentric.More or less spherical layers superimposed upon one another about a common center.
b) Pisolitic. Rounded masses about the size of peas.
c)Oolitic. A mineral aggregates formed of small spheres resembling fish roe.
d)Massive. Compact material without form or distinguishing features
e)Amygdaloidal. A rock such as basalt containing almond-shaped nodules.
f)Banded. A mineral in narrow bands of different color or textures.
CLEAVAGE, PARTING, AND FRACTURE
CLEAVAGE
A mineral has cleavage if it breaks along definite plane surfaces. Cleavage may be perfect as in the micas,or more or less obscure as in beryl and apatite. In some minerals, it is completely absent.
Cleavage depends on crystal structure and takes place parallel to atomic planes. If a family of parallel atomic planes has aweak binding force between them, cleavage is likely to take place along these planes. The weakness may be result of a weak type of a bond,agreater spacing between the planes, or a combination of the two. Graphite has platelikje cleavage. Within the plates there is a strong bond, but across the plates there is a weak bond giving rise to the cleavage. A weak bond is usually accompanied by a large interplanar spacing because the attractive force cannot hold the planes closely together. Diamond has but one bond type and its excellent cleavage take place along those atomic planes having the largest interplanar spacing.
Because cleavage is the breaking of a crystal between atomic planes, it is a directional property, and any parallel plane through a crystal is a potential cleavage plane. Moreover, it is always parallel to crystal faces or possible crystal faces, because both faces and cleavage reflect the same crystal structure.
In describing a cleavage its quality and crystallographic direction should be given. The quality is expressed as perfect,good, fair, etc. The direction is expressed by the name or indices of the form which the cleavage parallels, such as cubic (001), octahedral (111), rhombohedral (1011),prismatic (110) or pinacoidal (001).
Not all minerals show cleavage, and only a comparatively few show it in an eminent degree, but in these it serves as an outstanding diagnostic criterion.
Parting
When minerals break along planes of structural weakness, they have parting. The weakness may be result from pressure or twinning; and ,because it is parallel to rational crystallographic planes, it resembles cleavage. However, parting, unlike cleavage, is not shown by all specimens but only those that are twinned or have been subjected to the proper pressure. Even in these specimens there are a limited number of planes in a given direction along which the mineral will break. Familiar examples of parting are found in the octahedral parting of magnetite, the basal parting of pyroxene, and the rhomobohedral parting of corundum.










Fig: different kinds of cleavage. a) cubic, b) octahedral, c) Dodecahedral, d)Rhomohedral, e) prismatic and f) pinacoidal.
The figure also shows two kinds of parting: a) Basal parting, pyroxene b) Rhomohedral parting, corundum
Pycnometer is shown in the lower part of the figure




Fracture
The way a mineral breaks when it does not yield along cleavage orparting surfaces is fracture. Different kinds of fracture are designated as follows:
a. Conchoidal. The smooth, curved fracture resembling the interior surface of a shell. This is most commonly observed in such substances as glass and quartz.
b. Fibrous .
c. Hackly. Jagged fractures with sharp edges.
d. Uneven or irregular. Fractures producing rough and irregular surfaces.

HARDNESS
The resistance that a smooth surface of a mineral offers to scratching is its hardness (designated by H). Like the other physical properties of minerals, hardness is dependent on the crystal structure. The stronger the binding force between the atoms, the harder the mineral. The degree of hardness is determined by observing the comparative ease or difficulty with which one mineral is scratched by another, or by a file or knife. The hardness of a mineral might then be said to be its scratchability.
A series of 10 common minerals were chosen by Austrian mineralogist F. Mohs in 1824 as a scale, by comparison with the relative hardness of any mineral can be told. The following minerals arranged in order of increasing hardness comprise what is known as the Mohs scale of hardness:
1-Talc 6-Orthoclase
2-Gypsum 7-Quartz
3-calcite 8-Topaz
4-fluorite 9-Corundum
5-Apatite 10-Diamond
The relative position of the minerals in the Mohs scale is preserved, but corundum, for example, is two times as hard as topaz but four times harder than quartz.
Talc, number 1 in the Mohs scale, has a structure made up of plates so weakly bound to one another that the pressure of the fingers is sufficient to slide one plate over the other. At the other end of the scale is diamond with its constituent carbon atoms so firmly bound to each other that no other mineral can force them apart to cause a scratch.
In order to determine the relative hardness of any mineral in terms of this scale, it is necessary to find which of these minerals it can and which it cannot scratch. In making the determination, the following should be observed: sometimes when one mineral is softer the another, portions of the first will leave a mark on the second that may be mistaken for a scratch. Such a mark can be rubbed off, whereas a true scratch will be permanent. The surfaces of some minerals are frequently altered to material that is much softer than the original mineral. A fresh surface of the specimen to be tested should therefore be used.
The following materials serve in addition to the above scale: the hardness of the finger nail is a little over 2, a copper coin about 3, the steel of a pocket knife a little over 5, window glass 5.5, and the steel of file 6.5. With a little practice, the hardness of minerals under 5 can be quickly estimated by the ease with which they can be scratched with a pocket knife.

Streak
The color of a finely powdered mineral is known as its streak. Although the color of a mineral may vary, the streak is usually constant and is thus useful in mineral identification. The streak is determined by rubbing the mineral on a piece of unglazed porcelain, a streak plate. The streak plate has a hardness of about 7, and thus it cannot be used with minerals of grater hardness.

LUSTER
The term luster refers to the general appearance of a mineral surface in reflected light. There are two types of luster, metallic and nonmetallic, but with no sharp division between them. Minerals with an intermediate luster are said to be submetallic.
A mineral having the brilliant appearance of metal has ametallic luster. Such a minerals are quite opaque to light and, as a result, give a black or very dark streak. Galena, and chalcopyrite are common minerals with metallic luster.
Minerals with nonmetallic luster are, in general, light-colored and transmit light, if not through thick portions, at least through thin edges. The streak of a nonmetallic mineral is either colorless or very light in color. The following terms are used to describe further the luster of nonmetallic minerals:
Vitreous. The luster of glass. Examples-quartz and tourmaline
Resinous. Having the luster of resin. Examples-sphalerite and sulfur.
Pearly. An iridescent pearl-like luster. This is usually observed on mineral surfaces that are parallel to cleavage planes. Examples- cleavage surface of talc.
Greasy. Appears as if covered with a thin layer of oil. This luster results from light scattered by a microscopically rough surface. Examples, massive quartz, and some specimens of sphalerite
Silky. Silklike. It is caused by the reflection of light from a fine fibrous parallel aggregates. Examples-fibrous gypsum, malachite, and serpentine.
COLOR
When white light strikes the surface of a mineral, part of it is reflected and part refracted . If the light suffers no absorbtion, the mineral is colorless, both in reflected and transmitted light. Minerals are colored because certain wavelengths of light are absorbed, and the color results from a combination of those wavelengths that reach the eye. Someminerals show different colors when light is transmitted along different crystallographic directions. This selective absorbtion known as pleochrism is shown by transparent varieties of spodumene and corderite. If there are only two such directions, as in tourmaline, the property is called dichroism.
For some minerals, color is a fundamental property directly related to one of its major constituent elements and therefore constant and characteristic. For such minerals, called idiochromatic, color serves as an important means of identification. Thus malachite is always green, azurite is always red or pink.
For most metallic minerals, color is constant, as: the brass-yellow of chalcopyrite, the brownish bronze of bornite, and the copper-red of niccolite.
Because alteration may produce a colored tarnish on these minerals different from the true color, it is important that a fresh surface be examined. This is particularly true for copper minerals, especially bornite. This mineral is called peacock copper ore, because on exposure its bronze color is covered by a blue-violet film.
Most minerals are composed of elements that produce no characteristic color and are colorless. In some cases the color is attributable to appreciable amounts of an element, such as iron. For example, the amphibole tremolite, with composition Ca2Mg5 (Si8O22)(OH)2 is white but when some Fe2+ substitute for Mg2+, the mineral is green. With increasing amounts of iron, the color changes from pale to dark green to nearly black.
Minerals such as those mentioned that show a variation in color are called allochromatic. However, the presence of a major chemical constituent is only one of the causes of color in minerals. Other factors are small amounts of chemical impurities defects in crystal structure, and finely divided inclusions of other minerals.
Color in minerals with structure imperfections (due to structural voids),may be changed by heat treatment or exposure to high-energy radiation. For example, X-radiation turns some colorless quartz smoky, but on subsequent heating to 400ºC the quartz returns to its colorless state. Colorless diamonds by exposure to the proper radiation can be colored either green or blue, and the green diamond will turn yellow with heat treatment. The color of many other gem stones can be enhanced by heating.
The mechanical admixture of impurities can give a variety of colors to otherwise colorless minerals. Quartz me be green because of the presence of chlorite, calcite may be black colored by manganese oxide or carbon. Hematite, as the most common pigmenting impurity, imparts its red color to many minerals including some feldspar and calcite and the fine-grained variety of quartz.

Play of colors
Interference of light either at the surface or in the interior of a mineral may produce a series of colors as the angle of incident light changes. The striking play of colors seen in precious opal results from the



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