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Minerals
•
A mineral must:
1.
2.
3.
4.
5.
Occur naturally
Be a crystalline solid
Have a definite chemical composition
Possess characteristic physical properties
NOT be organic
Why aren’t the following minerals?
• Water
• Glass
Why aren’t the following minerals?
• Water
– it is a liquid at room temperature
• Glass
– It is not naturally occurring
Why aren’t the following minerals?
• Coal
Why aren’t the following minerals?
• Coal
–It is organic
–It lacks a definite chemical composition
–It does not have repeating structure
The Most Common Elements in the Earth’s
Crust
1.
2.
3.
4.
5.
6.
7.
8.
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
• These eight elements
make up 98.5% of
the Earth’s crust.
• Almost 94% of the
crust’s volume (not
mass) is oxygen.
Elements are not
distributed evenly
throughout the layers.
Not in your notes.
Not in your notes.
How Minerals Form
• Atoms in magma move about. As the magma
cools, movement slows and the atoms move
closer together. They bond chemically.
• The rate at which the magma cools
determines the size of the mineral grains.
• Dissolved atoms chemically link as water
evaporates.
COMMON MINERAL GROUPS
There are seven basic nonsilicate
mineral groups.
More than 90% of the minerals in the
crust and mantle are silicates.
NONSILICATE MINERALS
1. Native Elements
do not combine with other elements in nature.
Gold (Au)
Silver (Ag)
Platinum (Pt)
Diamond (C)
Graphite (C)
Sulfur (S)
Copper (Cu)
Gold
Copper
Silver
SILICATE MINERALS
• The two most abundant elements, silicon and
oxygen combine to form the basic building
block for most common minerals.
• Four oxygen atoms are packed together
around a single silicon atom.
• A silica tetrahedron is the result.
Silica tetrahedron
• Half the bonds are ionic.
• Half the bonds are covalent.
• It has an overall negative
charge.
• Tetrahedrons can link
together in different ways.
Silicates
• Combinations of oxygen and silicon plus
one other metallic element are called
silicates.
• They can exist independently, or as single
chains, double chains, sheets, or
frameworks.
Silica Tetrahedron
(blue = silicon; brown = oxygen)
4 oxygen anions are bonded to
a single silicon cation.
Silicon is positively charged
(+4)
Oxygen is negatively charged
(-2)
Net charge on tetrahedron: -4
Not in your notes.
Single Tetrahedron
X2SiO4
• Olivine
Two atoms of magnesium or iron balance the negative charge.
Single Chain
XSiO3
One atom of iron, magnesium, aluminum, or calcium balance the negative charge.
• Pyroxene
Note the fibrous appearance.
Single Chain Silicates
Adjacent tetrahedrons form a chain
by sharing 2 of their oxygen with
neighboring tetrahedrons.
E.g. pyroxenes (mafic silicates)
Not in your notes.
Double Chain
XSi8O22(OH)2
A combination of calcium, sodium, iron, magnesium, and aluminum
balance the negative charge.
• Amphibole
Double Chain Silicates
Two chains can link up by sharing
oxygen.
E.g. amphiboles (mafic silicates)
Not in your notes.
Sheet
KXAlSi3O10(OH)2
• Micas
– Biotite
– Muscovite
A magnesium, iron, and aluminum
balance the negative charge in biotite.
In muscovite only aluminum balances
the negative charge.
Sheet Silicates
Sheets are formed when each
tetrahedron shares 3 of its oxygen
with neighbors.
E.g. micas, clay minerals
Not in your notes.
Framework
• feldspar
KAlSi3O8 = orthoclase feldspar
a.k.a. potassium feldspar
Framework Silicates
Every oxygen in each tetrahedron is
shared to a form 3-D framework.
E.g. feldspar, quartz (non-mafic
silicates)
Not in your notes.
Identifying Minerals
Mineral properties
•
•
•
•
•
•
Colour
Luster
Habit (Shape)
Cleavage & Fracture
Streak
Hardness
Colour:
(Not mineral specific)
Quartz comes in a variety of
colours
Not in your notes.
Luster:
How minerals reflect light
Metallic
Nonmetallic
Metallic luster does not have to be shiny – It can look like a broken iron rod.
Mineral Habit (Shape)
Shape a mineral
takes if grown
unimpeded
Cleavage & Fracture
Cleavage: planes or surfaces of weakness
along which minerals can break
Fracture: surfaces other than cleavage
planes along which minerals can break
Examples of Cleavage
Not in your notes.
Cleavage & Fracture and resulting
crystal shape
Not in your notes.
Fracture
• Some minerals do not have cleavage but do
show a characteristic fracture.
• Fractures (irregular breaks) can sometimes
be distinctive
• When the fracture results in smooth, curved
surfaces, the sample is said to exhibit
“conchoidal” fracture
Quartz has conchoidal fracture
Not in your notes.
Crystalline Structure
• A crystal is a regular geometric solid with
smooth surfaces called crystal faces.
• The orderly arrangement of ions
determines the shape of the crystal.
• There are six basic crystal shapes
Streak:
The powdered form of a mineral when
rubbbed on an unglazed tile.
Hardness:
Is the resistance of a mineral to abrasion or
scratching.
Geologists use Moh’s scale of hardness.
Mohs Mineral Hardness Scale
1) Talc
Softest
2) Gypsum
3) Calcite
1
5
4) Fluorite
5) Apatite
2
6) Feldspar
6
7) Quartz
8) Topaz
3
7
9) Corundum
10) Diamond
9
Hardest
4
8
10
If this were an
absolute scale
diamond would
have a value of
40.
The hardest substance also produces the
softest substance, graphite.
As an example, calcite will scratch gypsum
and talc but not fluorite, apatite, or any of the
others.
Other Properties
• Specific gravity
• Reaction to acid
• Striations
• Magnetism