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Download Composition and Structure of Minerals
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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
