MINERALS AND ROCKS : Part 1

MINERALS

Minerals are naturally occurring substances that is solid and inorganic representable by a chemical formula usually abiogenic  (not produced by living organism) and has an ordered atomic structures.

TYPES OF ROCKS FORMING MINERALS

Fallowing are the various types of rocks forming minerals :-

1- SILICATES

It is very important minerals group and rock forming minerals. It is available in abundant due to l arge amount of silicon and oxygen in the earth crust’s.

COMMON SILICATES MATERIALS

OLIVINE :- Olivin is the high temperature Fe-Mg silicates called ferromagnesium. Individual tetrahedral linked together by ions and magnesium ions.

Olivins forms small rounded crystals with no cleavage.

PYROXENE GROUP

Pyroxene group has single chain structures involving iron and magnesium chains weakly paired. In Pyroxene Group two distinct cleavages at nearly 90 degrees.

AUGITE is the most common minerals in the Pyroxene groups.

AMPHIBOLE GROUP

It has a double chain structures involving a variety of ions.

In this group two perfect cleavages 

HOERNBLENDE is the most common minerals in the amphibole group.

 

MICA GROUP

Sheet structures that results in one direction of perfect cleavage .

BIOTITE is the most common dark coloured mica mineral and Muscovite is the common light mica mineral.

FELSPAR GROUP

Felspar group is the most common mineral group.

3-D frame work of tetrahedral exhibit two directions of perfect cleavage at 90 degrees.

Orthoclage and the Plagioclase are the two most commo minerals.

CLAY MINERALS

clay mineral all have a sheet or layered structure.

Most originate as the product of chemical weathering.

IMPORTANT NON SILICATES MINERALS

1- CALCITE (carbonate)

2- Haematite (oxide)

3- GALENA (sulphide)

4- GYPSUM (sulphate)

5- HALITE (halide)

6- PYRITE (sulphide)

PHYSICAL PROPERTIES OF MINERALS

1- 

2- STREAK

Streak is the colour of the minerals in the powdered form. Streak shows the true colour of the minerals.

In the large solid forms trace minerals can change the colour appearance  of a minerals by reflecting the light in a certain way.

3- HARDNESS

Hardness is the measure of the mineral’s hostility to scratch.

CLEAVAGE

Cleavage refers to the splitting of a  crystal along the smooth plane. A cleavage  is the tendency of rocks to split along a definite shape.

The quality of the minerals cleavage and  the character of the exposed surface.

FRACTURE

Fracture is the physical properties of the rock that determines  the quality of the cleavage surface .

Most minerals display either uneven or grainy fracture , conchoidal (curved , shell like lines ) fracture , or hacky (rough , jagged ) fracture

CRYSTALLINE STRUCTURE

Minerals crystals occurs in the various shapes and the sizes. The particular shapes are determined by the arrangements of the atoms , molecules or ions that makes up the crystal and how they are joined . This is called the crystal lattice.

There are many degrees of the structures that is crystallined, in which the fibers of the crystal are not seen by the naked eyes or the use of a hand lens.

LUSTER

Luster is the physical property of minerals that describes how much the surface of a minerals reflects the light .

ODOUR

Most mineral have no odor unless they acted upon in one of the fallowing ways  : moistened , heated , breathed upon , or rubbed

TASTE

Only soluble minerals have a taste , but it is very important that minerals not be placed in the mouth or on the tongue , it may harm because some minerals contain poisons.

 

 SPECIFIC GRAVITY

It is the ratio of the weight of the minerals to weight of an equal amount of water.

The weight of equal amount of water is obtain by determining the difference between the weight of the minerals in air and the weight of the minerals in the water.

PROCESS OF THE FORMATION OF THE MINERALS

Fallowing are the process of formation of the minerals in the nature are :-

1- Precipitation , Evaporation and weathering from a fluid

2- Sublimation from a vapor

3- Crystallization from a liquid

4- Solid – solid reaction

 

THE STRUCTURES EXHIBITED BY MINERALS

Fallowing are the few common structures forms observed in the minerals

1- TABULAR

The mineral in the form of flattened , square , rectangular or rhombohedral shape . In the other words flattening is conspicuous compared to lengthwise elongation .

Example :- calcite , orthoclase , barite , et cetera (etc)

2- ELONGATED

When the minerals is in the for of a thin or thick coloum like crystal . It is also commonly referred as the columnar structure.

Example :- beryl , quartz , hornblend.

3- BLEDED

The minerals appeared as if composed of the thin ,  blade-like overlapping .

Example : kyalite

4-  LAMELLAR

The minerals are of relatively thick , flexible , leaf like sheets.

Example : vermiculite

5-  FOLIATED

The structure is similar to lamellar in broader sense but in this case the individual sheets are paper thin , even thinner and can be easily separated.

Example : muscovite