Crystal Shapes

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Minerals
A Mineral is…
• Naturally Occurring – made by nature – not
by man
A Mineral is…
• Inorganic - not alive, never was alive, not
made from a living process
A Mineral is…
• Solid – not a liquid or a gas
A Mineral is…
• Unique Chemical Composition – every mineral
is different
A Mineral is…
• Crystalline Structure – atoms repeat in
patterns
Crystal Shapes
Basics of Crystals
• Crystals are defined by the number of sides
(faces) and the angles of these sides
(geometry)
1. Cubic
• cubic – all sides are square
2. Tetragonal
• tetragonal – 4 rectangles, 2 squares
3. Orthorhombic
• orthorhombic – all rectangles, 3 different sized
rectangles
4. Monoclinic
• monoclinic – 4 rectangles, 2 parallelograms
5. Triclinic
• triclinic – all parallelograms
6. Hexagonal
• hexagonal - six-sided prisms. When you look
at the crystal on-end, the cross section is a
hexagon
Mineral Groups
• Minerals are often grouped together by their
composition (what they are made of)
• There are over 4,000 known minerals and only
7 groups
1. Silicates (most common)
• Contain silicon and oxygen
• Ex. Quartz, Olivine, Augite
2. Carbonates
• Contain CO3
• Ex. Calcite, Dolomite
3. Oxides
• Contain oxygen bonded with 1 or more
elements
• Ex. Corundum, Hematite
4. Sulfides and 5. Sulfates
• Sulfides (contain Sulfur), Sulfates contain SO4
• Ex. Gypsum, Galena, Pyrite
6. Halides
• Contain halogens (Fluorine, Chlorine, etc.)
• Ex. Halite, Fluorite
7. Native Elements
• Mostly metals, found as individual elements
• Ex. Copper, Gold, Silver
How do Minerals form?
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•
•
•
1. Cooling magma or lava
2. Hydrothermal
3. Evaporation of liquid solutions
4. Precipitate out of solution
1. Cooling magma or lava
2. Hydrothermal
3. Evaporation of liquid solutions
4. Precipitate out of solution
5 Characteristics Used to Identify
Minerals
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•
•
•
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1) Hardness
2) Break Tendency
3) Luster (metallic/non-metallic)
4) Streak
5) Color
1) Hardness (Moh’s Scale)
• - how easily a mineral can be scratched
2) Break Tendency
• Fracture - breaks
along rough, jagged
edges
• Cleavage – breaks
along smooth, flat
surfaces
Conchoidal fracture – curved breakage
3) Luster (metallic/non-metallic)
• - how light shines off of its surface
• Metallic
Non-metallic
4) Streak
Color of a mineral when broken or
powdered
5) Color
Other ways to identify minerals
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•
•
•
Reactivity with acids
Density/specific gravity
Magnetism
More special properties to come
Other Properties of Minerals
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•
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•
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Reactivity with Acid
Magnetic
Fluorescence
Phosphouresence
Density
Crystal Shape
Triboluminesence
Reactivity with
acid
• Carbonate minerals
fizz when acid is
applied
Magnetic
• Some iron rich
minerals are
magnetic
Fluorescence
Phosphorescence
Triboluminesence
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