What exactly is a mineral??

What exactly is a Mineral??

Hey rockhounds!  At the request of a few members, I've quickly composed a brief description of what minerals are.  I hope it helps!

Minerals are typically defined as solid crystalline substances that are formed by natural (and usually inorganic) processes.  A mineral is characterized by homogenous phsyical properties, which means any two parts of the material will have the same properties.  These properties can vary with direction inside the crystal structure - for example a mineral might grow faster on one side than the other, or be harder on one side than the reverse - but this characteristic will be the same for any piece of that mineral.

Every mineral has a distinct chemical composition which can very within certain limits, but is always clearly defined.

Minerals also have distinct crystal structures.  What's that mean?  The atoms that make up the mineral are arranged in a regular and repeating three dimensional network or pattern.  No matter where a sample is taken from the crystal, the atomic arrangement will always be the same. 

Some minerals share the same atomic arrangement of atoms, with different types of atoms comprising the structure.  This is known as 'isotypism'.

Not all minerals are formed from inorganic processes, for example, some types of limestone - rocks that are essentially formed from calcite - come from animal and vegetable marine organism accumulation.  This calcite is usually considered a mineral because its usually identical with calcite formed by inorganic process and deformation and recrystalization usually occur in the formation of limestone.  Deformation and recrystalization are both considered inorganic processes.