MINERALS & ROCKS MINERALS & ROCKS
A mineral is a naturally occurring substance that is solid and stable at room temperature, representable by a chemical formula, usually abiogenic, and has an ordered atomic structure
Mineral are divided as follows:
A. Metallic Minerals
These minerals contain metal content and can be sub-divided into three types: (i) Precious metals: gold, silver, platinum etc. (ii) Ferrous metals: iron and other metals often mixed with iron to form various kinds of steel.
(iii) Non-ferrous metals: include metals like copper, lead,
B. Non-Metallic Minerals
These minerals do not contain metal content. Sulphur, phosphates and nitrates are examples of non-metallic minerals. Cement is a mixture of non-metallic minerals.
Some Major Minerals and Their Characteristics • Feldspar Silicon and oxygen are common elements in all types of feldspar and sodium, potassium, calcium, aluminium etc. are found in specific feldspar variety. Half of the earth’s crust is composed of feldspar. It has cream to salmon pink colour. It is used in ceramics industries.
It is one of the most important components of sand and granite. It consists of silica. It is a hard mineral virtually insoluble in water. It is white or colourless and used in radio and radar. It is one of the most important components of granite. • Pyroxene Pyroxene consists of calcium, aluminum,magnesium, iron and silica. Pyroxene forms 10 per cent of the earth’s crust. It is commonly found in meteorites. It is in green or black colour.
Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles. They form 7 per cent of the earth’s crust. It is in green or black colour and is used in asbestos industry. Hornblende is another form of amphiboles.
It comprises of potassium, aluminium, magnesium, iron, silica etc. It forms 4% of the earth’s crust. Commonly found in igneous and metamorphic rocks, it is used in electrical instruments.
Magnesium, iron and silica are major elements of olivine. It is used in jewellery. It is usually a greenish crystal, often found in basaltic rocks. Other minerals like chlorite, calcite, magnetite, haematite, bauxite and barite are also present in some quantities in the rocks.
the earth’s crust is composed of rocks. A rock is an aggregate of one or more minerals. Rock may be hard or soft and in varied colours. For example, granite is hard, sandstone is soft. Gabbro is black and quartzite can be milky white. Rocks do not have definite composition of mineral constituents. Feldspar and quartz are the most common minerals found in rocks.
The crustal rocks are classified on the basis of mode of formation, physical and chemical properties, location etc. On the basis of mode of formation the rocks are divided into three categories (i) igneous rocks (ii) sedimentary rocks (iii) metamorphic rocks.
A) Igneous rocks
As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks. The igneous rocks are formed when magma cools and solidifies. When magma in its upward movement cools and turns into solid form it is called igneous rock. The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth.
Igneous rocks are characterized on the basis of texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
Igneous rocks are roughly hard rocks and water percolates with great difficulty. They do not have strata and are less affected by chemical weathering. They don’t contain fossils. The number of joints increases upwards. They are mostly associated