A mineral, is defined as, a naturally occurring inorganic solid substance that is characterized with a definite chemical composition and very often with a definite atomic structure.

Some minerals may show rainbow colours eir in ir interior or on exterior surface. This is called iridescence.

Amorphous form is a form in which neir a crystal face nor a cleavage is seen. There is no evidence of orderly arrangement of atoms in this form.

Amethyst quartz, agate and jasper belong to quartz group, whereas, calcite belongs to carbonate group whose chemical composition is completely different compared to quartz group.

One of main trait of quartz group is that minerals do not give any streak though are present in many colours in appearance.

The calcite minerals are known to show three sets of cleavage which is pretty distinctive compared to or mineral groups.

Phosphorescence is similar to fluorescence in essential character but in this case light is emitted by mineral not during act of exposure but after substance is transferred rapidly to a dark place. Fluorite, quartz, willemite and diamond show this phenomenon.

Magnesite mineral is found is colours like white, shades of grey and also sometimes brown. But when it is in pure form, it is found in bone white colour.

Gypsum is found usually in translucent and sometimes in opaque forms. In its pure form it is found in translucent form.

Mammillary is similar to globular but projections are conspicuous in size, overlapping in arrangement and rounded in shape, best example is malachite.