1. MINERALS

2. Minerals are the solid constituents of all rocks, igneous, sedimentary and metamorphic and occur as crystals.
Definition of Mineral
A mineral can be defined as a natural inorganic substance having a particular chemical composition or range of composition, and a regular atomic structure to which its crystalline form is related.
Before beginning the study of rocks it is necessary to know something of the chief rock-forming minerals.

3. Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions.

5. The average composition of crustal rocks is given in Table 4
The average composition of crustal rocks is given in Table 4.1 and has been calculated from many chemical analyses.
The last item includes the oxides of other metals; and also gases such as carbon dioxide, sulphur dioxide, chlorine, fluorine, and others; and trace elements, which occur in very small quantities.

7. Properties of Minerals
Included under this head are properties such as colour, lustre, form, hardness, cleavage, fracture, tenacity, and specific gravity.
Not all of these properties would necessarily be needed to identify anyone mineral; two or three of them taken together may be sufficient, apart from optical properties .

8. Colour
Color is one of the physical properties most commonly used to describe minerals, but it is not a very good property to use to identify minerals .
Some minerals are nearly always the same color like azurite (blue) and sulfur (yellow)
Many minerals come in a variety of colors – the changes are caused by slight chemical impurities or through exposure to heat.
Thus quartz, which is colourless when pure, may be white, grey, pink or yellow, when certain chemical impurities or included particles are present.

9. Streak
A mineral powder form may have different colour from individual crystals. This can be an important feature for identification.
This may be produced by rubbing the mineral on a piece of unglazed porcelain, called a streak-plate, or other rough surface.
Streak is useful, for example, in distinguishing the various oxides of iron; haematite gives a red streak, limonite a brown, and magnetite a grey streak.

10. Magnetite a grey streak
Limonite a brown

11. Glassy or vitreous, as in quartz
Lustre
Lustre is the appearance of a mineral surface in reflected light.
Lustre is how the mineral reflects light.
It may be described as metallic, as in pyrite or galena; glassy or vitreous, as in quartz; resinous or greasy, as in opal; pearly, as in talc; or silky, as in fibrous minerals such as asbestos and satin-spar (fibrous gypsum). Minerals with no lustre are described as dull.
Glassy or vitreous, as in quartz
Metallic, as in pyrite

12. resinous or greasy, as in opal
pearly, as in talc

13. Silky lustre as in fibrous asbestos
Dull lustre

14. Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, ...

16. Specific Gravity
Specific Gravity, also known as SG, is a measurement that determines the density of minerals.
Two minerals may be the same size, but their weight may be very different. The specific gravity of a mineral determines how heavy it is by its relative weight to water.
Minerals with a specific gravity under 2 are considered light, between 2 and 4.5 average, and greater than 4.5 heavy. Most minerals with a metallic luster are heavy.
The specific gravity may slightly vary within a mineral because of impurities present in the minerals structure.

17. Specific Gravity of minerals range from 1 to over 20 in specific gravity (e.g. native platinum, 21.46), but most lie between 2 and 7.

18. Separation of mineral fragments using specific gravity
The separation of fragments of a particular mineral from a sediment containing many minerals may be achieved by placing them in a liquid solution of known specific gravity equal to that of the mineral to be separated. Grains of greater specific gravity than the liquid will sink whilst those of lower specific gravity will float.

19. Cleavage
Many minerals possess a tendency to split easily in certain regular directions, and yield smooth plane surfaces called cleavage planes when thus broken. These directions depend on the arrangement of the atoms in a mineral and are parallel to definite crystal faces.
Perfect, good, distinct, and imperfect are terms used to describe the quality of mineral cleavage.
Mica, for example, has a perfect cleavage by means of which it can be split into very thin flakes; feldspars have two sets of good cleavage planes. Calcite has three directions of cleavage.

22. Form
Under this heading come a number of terms which are commonly used to describe various shapes assumed by minerals in groups or clusters.
Botryoidal - consisting of spheroidal aggregations, somewhat resembling a bunch of grapes; e.g. chalcedony.
The curved surfaces are boundaries of the ends .
Reniform - kidney-shaped, the rounded surfaces of the mineral resembling those of kidneys; e.g. kidney iron ore, a variety of haematite.

25. Tabular - showing broad flat surfaces; e. g
Tabular - showing broad flat surfaces; e.g. the 6-sided crystals of mica.
Dendritic - moss-like or tree-like forms, generally produced by the deposition of a mineral in thin veneers on joint planes or in crevices; e.g. dendritic deposits of manganese oxide.
Acicular - in fine needle-like crystals (also described as filiform).
Concretionary or nodular - terms applied to minerals found in detached masses of spherical, ellipsoidal, or irregular shape.

26. Tenacity
The response of a mineral to a hammer blow, to cutting with a knife and to bending is described by its tenacity.
Minerals that can be beaten into new shapes are malleable; e.g. the native metals of gold, silver and copper.
Most minerals are brittle and fracture when struck with a hammer.
Flakes of mica can be bent and yet return to their flat tabular shape when free to do so: they are both flexible and elastic: cleavage flakes of gypsum are flexible but inelastic.