5-2 composition and structure of minerals
Post on 17-Jan-2016
11 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
top related