Mineral Formation and Structure
Characteristics of Minerals
·
A mineral is a natural, inorganic solid with a
definite chemical composition and a particular crystalline structure
·
Characteristics
o 1. A mineral is formed in nature
o 2. A mineral is inorganic
o 3.
A mineral is a solid
o 4. A mineral has a definite composition
o 5. A mineral has a particular crystalline
structure
Mineral Formation
·
Minerals are formed slowly by two natural
processes
o Cooling
of Magma
§
Magma rises and falls in cracks in crust
·
Forms crystals
§
Cools slowly:
large crystals
§
Cools rapid:
small crystals
§
Ex:
olivine, plagioclase, feldspar, quartz
o Precipitation
§
Liquid part of a mineral-containing solution
evaporates: the mineral is left
behind (called precipitate)
§
Largest mineral solution: Ocean
·
Many minerals have chemical similarities and are
put into groups
·
Major Mineral groups (ex.’s on pg. 188)
o Silicates: Si + O + one or more metals
o Carbonates: CO3 + one or more metals
o Sulfates: SO4 + one or more metals
o Oxides: O + one or more metals
o Halides: Cl or F + a metal
Crystal Structure
·
Shapes of crystals of the Earth’s minerals are
classified into 6 groups
·
Crystal shape is determined by the arrangement of
the atoms that make up the mineral
·
Shape of mineral’s crystals are always the same no
matter how large/small
·
Basic Crystal Systems (pictures on pg. 189)
o Cubic: 3 axes of equal length intersect at 90° angles
o Tetragonal: same as cubic, except the vertical axis is
longer or shorter than the others
o Orthorhombic: 3 axes of different lengths intersect at 90° angles
o Monoclinic: same as orthorhombic except 1 axis is
oblique (not at 90°)
to the others
o Triclinic: 3 unequal axes intersect at oblique angles
to one another
o Hexagonal: 3 equal horizontal axes intersect at 60° angles; the
vertical axis is longer or shorter than the others.