Transcript Structure of Minerals

Structure of Minerals
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All minerals are crystalline
The atoms are arranged in a regular
pattern
A crystal is a regular geometric solid with
smooth surfaces called crystal faces
The orderly arrangement of ions
determines the shape of the crystal.
Crystal Structure
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Each kind of mineral has its own crystal
form.
Halite (NaCl) typically forms a crystal in the
shape of a cube
Quartz (SiO2) may form long, regular six
sided crystals.
The angles at which crystal faces meet is
always the same for each kind of mineral.
To describe these shapes crystallographic
axes are used. They are drawn
perpendicular to crystal faces.
Six Crystal Systems
Silica Tetrahedron
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More than 90% of the minerals in Earth’s
crust are members of a mineral family
called silicates.
They are compounds of silicon and oxygen
plus one or more metallic element such as
aluminum or iron
In all silicates the basic building block is
four O atoms packed closely around a Si
atom, held together by covalent bonds.
The basic unit forms a silica tetrahedron
Silicates are classified according to the way
the tetrahedrons are linked. Fig 3.16 p. 40
Crystals and Physical Properties
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The orderly arrangement of the atoms or
ions helps explain the other properties of
the mineral.
A mineral is a solid because of the close
packing of its ions or atoms and the strong
forces of attraction between them
The hardness of a mineral depends on the
arrangement of its ions or atoms
Carbon forms diamond, the hardest natural
mineral.
Carbon also forms graphite, a very soft
mineral that flakes easily
Carbon atoms are arranged in layers or
sheets in the graphite structure.
Diamond and Graphite
Diamond structure