Minerals A mineral must: 1.Occur naturally 2.Be a crystalline solid 3.Have a definite chemical...
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Transcript of Minerals A mineral must: 1.Occur naturally 2.Be a crystalline solid 3.Have a definite chemical...
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Minerals
• A mineral must:1. Occur naturally2. Be a crystalline solid3. Have a definite chemical composition4. Possess characteristic physical
properties5. NOT be organic
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Why aren’t the following minerals?
• Water
• Glass
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Why aren’t the following minerals?
• Water
– it is a liquid at room temperature
• Glass
– It is not naturally occurring
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Why aren’t the following minerals?
• Coal
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Why aren’t the following minerals?
• Coal
–It is organic–It lacks a definite chemical composition–It does not have repeating structure
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The Most Common Elements in the Earth’s Crust
1. Oxygen2. Silicon3. Aluminum4. Iron5. Calcium6. Sodium7. Potassium8. Magnesium
• These eight elements make up 98.5% of the Earth’s crust.
• Almost 94% of the crust’s volume (not mass) is oxygen.
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Elements are not distributed evenly throughout the layers.
Not in your notes.
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Not in your notes.
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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.
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COMMON MINERAL GROUPSThere are seven basic nonsilicate mineral groups.
More than 90% of the minerals in thecrust and mantle are silicates.
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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)
NONSILICATE MINERALS
Copper
Silver
Gold
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• 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.
SILICATE MINERALS
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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.
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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.
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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: -4Not in your notes.
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Single Tetrahedron
• Olivine
Two atoms of magnesium or iron balance the negative charge.
X2SiO4
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Single Chain
• Pyroxene
Note the fibrous appearance.
XSiO3
One atom of iron, magnesium, aluminum, or calcium balance the negative charge.
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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.
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Double Chain
• Amphibole
XSi8O22(OH)2
A combination of calcium, sodium, iron, magnesium, and aluminum balance the negative charge.
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Double Chain Silicates
Two chains can link up by sharing oxygen.
E.g. amphiboles (mafic silicates)
Not in your notes.
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Sheet
• Micas– Biotite–Muscovite
KXAlSi3O10(OH)2
A magnesium, iron, and aluminum balance the negative charge in biotite. In muscovite only aluminum balances the negative charge.
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Sheet Silicates
Sheets are formed when each tetrahedron shares 3 of its oxygen with neighbors.
E.g. micas, clay minerals
Not in your notes.
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Framework
• feldspar
KAlSi3O8 = orthoclase feldspara.k.a. potassium feldspar
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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.
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Identifying Minerals
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Mineral properties• Colour• Luster• Habit (Shape)• Cleavage & Fracture• Streak• Hardness
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Colour:(Not mineral specific)
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Quartz comes in a variety of colours
Not in your notes.
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Luster:How minerals reflect light
Non-metallic
Metallic
Metallic luster does not have to be shiny – It can look like a broken iron rod.
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Mineral Habit (Shape)
Shape a mineral takes if grown unimpeded
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Cleavage & FractureCleavage: planes or surfaces of
weakness along which minerals can break
Fracture: surfaces other than cleavage planes along which minerals can break
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Examples of Cleavage
Not in your notes.
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Cleavage & Fracture and resulting crystal shape
Not in your notes.
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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
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Quartz has conchoidal fracture
Not in your notes.
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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
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Streak:The powdered form of a mineral when rubbbed on an unglazed tile.
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Hardness:Is the resistance of a mineral to abrasion or scratching.
Geologists use Moh’s scale of hardness.
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Mohs Mineral Hardness Scale1) Talc
2) Gypsum
3) Calcite
4) Fluorite
5) Apatite
6) Feldspar
7) Quartz
8) Topaz
9) Corundum
10) Diamond
Softest
Hardest
1
2
3
4
5
6
7
8
9
10
If this were an absolute scale diamond would have a value of 40.
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As an example, calcite will scratch gypsum and talc but not fluorite, apatite, or any of the others.
The hardest substance also produces the softest substance, graphite.
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Other Properties• Specific gravity• Reaction to acid• Striations• Magnetism