GEO 101 Lecture Notes - Lecture 4: Mohs Scale Of Mineral Hardness, Amorphous Solid, Standard Scale
21 Feb 2018
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Minerals- naturally occurring solid (minerals are only produced in
nature), formed by geological processes, has crystalline structure, and
has defined inorganic composition
• Minerals are the building blocks for rocks- most rocks are
made up of the same minerals but some different
• Solid- they have their own shape
• Crystalline structure- the atoms of the mineral are organized
in a specific pattern referred to as a crystalline lattice
o Glass- considered a liquid because it has amorphous
solid structure unlike minerals
• Inorganic composition- there is a chemical formula that can
be written, the chemical composition is inorganic (no carbon)
o Graphite and Diamond are made of carbon but are still
minerals---Polymorphs-minerals with the same
chemical composition but different atomic arrangement
• Composition of minerals
o Element- building blocks of minerals, more than 100
elements
o Atoms- smallest particle of matter
Rocks/sediment---minerals---molecules/atoms
• Structure of Minerals- symmetry in a specific minerals
structure, most common structure is tetrahedron
• How do we identify minerals?
o By observation
o Performing simple tests
o System of several physical properties are used to
identify samples of minerals---Primary Diagnostic
Properties
▪ Crystalline Form- external expression of mineral’s
internal structure
▪ Luster- appearance in reflected lights
Metallic vs. Nonmetallic
▪ Color- generally unreliable for mineral ID due to
variety of impurities, coloration of minerals
produce gemstones
Change in color can be changed due to
aging or by inclusions between the
tetrahedron
▪ Streak- color of a mineral in its powdered form
(can be different), obtained by scratching the
mineral on a porcelain plate
▪ Hardness- resistance of a mineral to scratching or
abrasion, all minerals are compared to a standard
scale called Mohs Hardness Scale
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