Minerals

What Exactly are Minerals?

A mineral is an inorganic solid which has occurred naturally through a geological process. It must have a specific chemical composition and distinctive internal crystal structure. Something that's inorganic cannot contain any living matter. Minerals are made up of ninety two different elements, an element which is made up of atoms are chemically the simplest substances which means they cannot be broken down through a chemical reaction.  A chemical reaction causes a substance to change into one or more different substances.  Although minerals can be made up of one single element the vast majority are made up of at least two.  Those made up of one are known as native elements and include copper, aluminium, carbon, iron, lead, vanadium and silver to name just a few.  When a substance is made up of two or more chemical elements it becomes known as a chemical compound.

The word crystalline is used to describe a solid that has a crystal structure so something described as being crystalline is a mineral.  A crystal structure is an arrangement of atoms that come together in a highly ordered three-dimensional pattern which forms a solid body known as a crystal.The arrangement of atoms within the crystal is known as a crystal lattice.  Naturally occurring solids that do not have a significant crystal structure cannot be classified as minerals and are instead known as mineraloids.  Some of the best known mineraloids include amber which is fossilised tree resin, shungite, moldavite, opal, pearl and obsidian which is volcanic glass. 

Most of the rocks on our planet are made up of several different minerals but some such as calcite and quartzite are made up primarily of one single mineral.   Most of the geological processes that take place on Earth are the result of processes that take place inside minerals. 

Although there are close to 4000 minerals which have been identified only about 100 are classified as being common.  Whilst identifying a mineral can sometimes be quite straightforward it can also be extremely difficult.  Colour is usually a good place to start but it can be the most unreliable method because many minerals occur in a variety of different colours a good example being quartz, some exhibit a range of several different colours or shades of colour and specific colour of the same mineral can change from one stone to the next.  Furthermore colour may also be caused by impurities of other minerals an example being the purple in amethyst which is caused by the presence of iron or the green colour in emerald which is caused by chromium and vanadium.

Streak and lustre may also be used for identification purposes.  Streak is the term used to describe the colour of a mineral in powdered form and the colour of a mineral's streak never changes.  In malachite it's green which some would say is to be expected because malachite is a green mineral but the streak in hematite which most people know as a steely grey coloured stone is red.  Hematite is a common iron oxide mineral whose name came about because of the blood red colour of its streak.

Lustre is the term used to describe the way that light reflects off the surface of a mineral and whilst there are several different types of lustre, vitreous is the one that tends to be used most often. 

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