Composition and Structure of Minerals In order to be classified as a mineral a substance has to be

• Naturally occurring • Solid • Definite chemical composition • Orderly pattern of atoms (crystal) • Inorganic Mineral Facts

• 4000 known minerals • Eight minerals make up >98% of the Earth’s crust • Most are compounds • Some are native elements • Rocks are mixtures of minerals Mineral Formation • From magma – As magma cools and hardens chemical bonds form – More than one mineral is produced from the same magma due to types of elements and cooling times Minerals formed from magma

Gabbro is a volcanic rock that contains quartz, feldspar and mica (minerals) Mineral Formation • From dissolved ions • Water evaporates, leaving minerals behind Evaporates

Form when water evaporates and leaves mineral crystals behind like salt Mineral Formation • Existing minerals are transformed by heat and pressure

Structure of Minerals

• Crystal structure – Regular, geometric, smooth faces – Orderly arrangements with repeating structures – Each mineral always forms the same crystal shape – Six basic crystal shapes – Crystallographic axes are used to determine structure Mineral crystals Crystallographic Axis Silicates

• Most numerous • Contain Si and O (and a metal) • Forms a silica tetrahedron • Covalent bond Depending on the arrangement of the silica tetrahedron, different groups of silicates will form. Crystal Structure

• Determines cleavage – Split occurs where bonds are weak – Halite: cubic cleavage – Quartz: no cleavage Hardness

• Depends on arrangement of ions, atoms or molecules and strength of bond – Carbon can form diamonds in a tetrahedron – Carbon can form graphite in a hexagonal arrangement