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Geology
Chapter 5 Minerals of Earth’s
Crust
5.1 What is a Mineral?
5.1 What is a Mineral Objectives
• Define mineral.
• Compare the two main groups of minerals.
• Identify the six types of silicate crystalline
structures.
• Describe three common nonsilicate
crystalline structures.
Introduction
• A mineral is a natural,
usually inorganic solid
that has a
characteristic
chemical composition,
an orderly internal
structure, and a
characteristic set of
physical properties.
Pyrite Sun - Illinois
Characteristics of Minerals
• An item must pass the “four questions” to
be considered a mineral.
– Is it inorganic?
– Does it occur naturally?
– Is it a crystalline solid?
– Does it have a consistent chemical
composition?
• If the answer is yes to all the above
questions, the item is a mineral.
Characteristics of Minerals
Kinds of Minerals
• More than 3,000 kinds of minerals have been
identified.
• Fewer than 20 minerals are common – they are
called the rock forming minerals.
• Only 10 of the rock forming minerals make up
90% of the Earth’s crust.
• Based on their chemical composition, minerals
can be classified into one of two groups –
silicate minerals and nonsilicate minerals.
Kinds of Minerals
• Silicate minerals contain a combination of silicon
and oxygen, and they may contain one or more
metals.
• For example…
– quartz is made only from silicon and oxygen
– feldspar, the most common silicate contains
potassium (potassium feldspar) or sodium or calcium
– or both (plagioclase feldspar)
– ferromagnesian minerals are rich in iron and
magnesium
– Feldspar and quartz alone make up 50% of the
Earth’s crust
Kinds of Minerals
• Nonsilicate minerals do not contain silicon and
oxygen and make up about 4% of the Earth’s
crust.
• Nonsilicate minerals are divided into six major
categories by their chemical composition.
–
–
–
–
–
–
Carbonates – contain carbonate group (CO3)
Halides – Cl or F combined with Na, K, or Ca
Native elements – pure elements
Oxides – contain oxygen, but no silicon
Sulfates – contain sulfate group (SO4)
Sulfides – one or more elements combined with sulfur
Crystalline Structure
• A crystal is a solid whose
atoms, ions, or molecules
are arranged in a regular,
repeating pattern.
• The characteristic
geometry of a crystal’s
internal structure can be
seen in large mineral
crystals that grow
uninhibited.
• Minerals are commonly
made up of masses of
microscopic crystals.
Beryl Crystal in Quartz - Brazil
Crystalline Structure of Silicate
Minerals
• The silicon-oxygen
tetrahedron is the
basic unit of the
structure of silicate
minerals; a silicon ion
chemically bonded to
and surrounded by
four oxygen ions.
http://www.winona.edu/geology/MRW/mrwi
mages/tetrahedron.jpg
Crystalline Structure of Silicate
Minerals
• Silicon-oxygen tetrahedra combine in a variety of
arrangements to form different silicate minerals.
– Isolated tetrahedra – do not link with other silicon or oxygen
atoms
– Ring silicates – form rings by sharing oxygen atoms
– Single-chain silicates – form a chain by sharing oxygen atoms
– Double-chain silicates – form when two single chains of
tetrahedra bond to each other
– Sheet silicates – form when each tetrahedron shares three of it s
oxygen atoms with other tetrahedra
– Framework silicates – form when each tetrahedron is bonded to
four other tetrahedra
*See Figure 3 pg. 107.
Six Kinds of Silicate Mineral
Arrangements
Six Kinds of Silicate Mineral
Arrangements
Six Kinds of Silicate Mineral
Arrangements
The Crystalline Structure of
Nonsilicate Minerals
• Nonsilicate minerals
display a variety of
crystal structures
including cubes,
hexagonal prisms, and
irregular masses.
• The structure of the
nonsilicate mineral
determines the
characteristics of that
mineral.
Dogtooth Calcite – Unknown
Origin
The Crystalline Structure of
Nonsilicate Minerals
• In native elements, for
example, atoms are
packed together as close
as possible (closest
packing).
• Closest packing results in
the higher densities of
metals.
• Each metal atom may be
surrounded by 8 to 12
other metal atoms which
are as close to each other
as the charges of the
atomic nuclei will allow.
Native Copper - Michigan