Composition and Structure of Minerals
Transcript of Composition and Structure of Minerals
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Composition and Structure of Minerals
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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
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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
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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
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Minerals formed from magma
Gabbro is a volcanic rock that contains quartz,
feldspar and mica (minerals)
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Mineral Formation • From dissolved ions
• Water evaporates, leaving minerals behind
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Evaporates
Form when water evaporates and leaves mineral
crystals behind like salt
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Mineral Formation • Existing minerals are transformed by heat
and pressure
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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
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Mineral crystals
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Crystallographic Axis
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Silicates
• Most numerous
• Contain Si and O (and a metal)
• Forms a silica tetrahedron
• Covalent bond
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Depending on the arrangement of the silica tetrahedron, different
groups of silicates will form.
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Crystal Structure
• Determines cleavage
– Split occurs where bonds are weak
– Halite: cubic cleavage
– Quartz: no cleavage
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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