Gypsum crystals

Gypsum crystals, 007358

A mineral is a solid naturally occurring substance with a crystalline structure and a composition specific to that mineral.  It has an atomic arrangement specific to its mineral variety.  On a whole, they are inorganic elements or compounds which form through a process known as crystallisation.

An example of minerals crystallising are those within a magma chamber, which start to crystallise as it cools.  The first minerals to start cooling and crystallising into a crystal mush are feldspar and olivine.

We identify minerals by testing different properties. These properties are as follows:

  • Hardness – which is measured on the Mohs hardness scale 1 to 10 (diamond is the hardest and talc is the softest)
  • Fracture – which is how many planes of cleavage (surfaces) the specimen will break along
  • Streak – which is the colour of the powder it would leave when rubbed on a ceramic streak plate
  • Colour of the mineral under natural light
  • Lustre – which is how the mineral reflects the light
Smokey quartz crystals

Smokey quartz, 007182

Silicates are the most common form of mineral, with more than 95% of minerals falling into this category.  This includes many rock forming minerals including quartz, feldspar, hornblende and pyroxene.  Other types of mineral include carbonates, sulphates, halides, oxides, sulphides and phosphates.

Minerals are useful with the identification of rocks because rocks have a certain mineralogical content.  They also aid with identifying the temperatures at which an igneous rock may have formed or when a metamorphic rock was being heated.  This is because certain minerals alter at certain temperatures.

Minerals have many uses which you wouldn’t expect, for example did you know that muscovite mica is used in irons and toasters.

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