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Tarbuck, Lutgens, Tsujita, Hicock, Earth:
An Introduction to Physical Geology 3Ce
Chapter 2: Minerals: the Building
Blocks of Rocks
Copyright © 2012 Pearson Canada Inc.
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Minerals:
The Building Blocks of Rocks
• Definition of a mineral:
• Naturally occurring
• Inorganic
• Solid
• Ordered internal molecular structure
• Definite chemical composition
• Definition of a rock:
• A solid mass of minerals
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The Composition of Minerals
• Elements
• Basic building blocks of minerals
• 113 are known now (90 naturally
occurring)
• Atoms
• Smallest particles of matter
• Retains all the characteristics of an
element
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The Composition of Minerals
• Atomic structure
• Central region called the nucleus
– Consists of protons (positive charges) and
neutrons (no electrical charges)
• Electrons
– Negatively charged particles that surround
the nucleus
– Located in discrete energy levels called
shells
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The Composition of Minerals
• Atomic structure
– Atomic number – number of protons in the
atom
– Atomic weight – approximately the total
number of protons and neutrons in the
nucleus
– Valence electrons – outer most electrons
in the shell
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The Composition of Minerals
• Bonding
– Chemical bonds – strong attractive force
forms compounds
– Ionic bonds – attraction of oppositely
charged ions producing electrically neutral
compound
– Covalent bonds – bonds that share
electrons
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The Structure of Minerals
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The Structure of Minerals
• A mineral consists of an ordered array
of atoms chemically bonded to form a
particular crystalline structure
• Polymorph – some elements can join in
more than one geometric arrangement
– Chemical composition stays the same
– Physical properties differ
– Example: diamond and graphite
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The Structure of Minerals
Diamond and graphite are polymorphs of carbon.
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Physical Properties of Minerals
• Crystal habit (shape)
• External expression of the orderly
internal arrangement of atoms
• Crystal growth is often interrupted
because of competition for space and
rapid loss of heat
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Physical Properties of Minerals
• Lustre
• Appearance of a mineral in reflected
light
• Two basic categories
– Metallic
– Nonmetallic
• Other terms, such as vitreous, silky, or
earthy, are used to further describe
nonmetallic lustre
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Physical Properties of Minerals
• Colour
• Often obvious (yellow, pink etc) but not
diagnostic if used for ID alone.
• Slight impurities can produce strong
colour variations.
Example: Quartz – can be clear, white,
rose, smoky, purple etc.
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Physical Properties of Minerals
Quartz (SiO2) exhibits a variety of colours as in the purple amethyst.
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Physical Properties of Minerals
• Streak
• Colour of a mineral in its powdered form
when rubbed on an unglazed porcelain
tile (streak plate)
• Hardness
• Resistance of a mineral to abrasion or
scratching
• All minerals are compared to a standard
scale called the Mohs scale of hardness
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Physical Properties of Minerals
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Physical Properties of Minerals
• Cleavage
• Tendency to break along planes of weak
bonding
• Produces flat, shiny surfaces
• Described by resulting geometric
shapes
– Number of planes
– Angles between adjacent planes
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Physical Properties of Minerals
• Fracture
• Absence of cleavage when a mineral is
broken
• Conchoidal fracture – breaks to form
smooth curved surfaces like broken
glass
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Physical Properties of Minerals
• Specific gravity
• Ratio of the weight of a mineral to the
weight of an equal volume of water
• Average value is approximately between
2.5 and 3
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Physical Properties of Minerals
• Other properties (“special properties”)
• Magnetism
• Reaction to hydrochloric acid
• Malleability
• Double refraction
• Taste
• Smell
• Elasticity
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Mineral Classes
• Nearly 4000 minerals have been
identified
• Rock-forming minerals
• A few common minerals that make up
most of the rocks of Earth’s crust
• Composed mainly of the 8 elements
that make up over 98% of the
continental crust
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Mineral Classes
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Mineral Classes
• The Silicates
• Most common mineral group
• Basic building block is the siliconoxygen tetrahedron
– Four oxygen ions surrounding a much
smaller silicon ion to form a more complex
ion
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Mineral Groups
• More complex Silicate structures
• Tetrahedra are linked together to form
various structures including:
• Single chains
• Double chains
• Sheet structures
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Common Silicate Minerals
• Ferromagnesian (dark) silicates
• Olivine group
• Pyroxenes – includes augite
• Amphiboles
• Biotite
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Common Silicate Minerals
• Nonferromagnesian (light) silicates
• Mica Group
– Muscovite is the common light coloured
mica
• Feldspar
– Orthoclase (potassium feldspar)
– Plagioclase
• Quartz
• Clay
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Mineral Classes
• Important nonsilicate minerals
• Several major groups exist including
– Oxides
– Hydroxides
– Sulphides
– Sulphates
– Native Elements
– Halides
– Carbonates
– Phosphates
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Mineral Classes
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Gemstones
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