objectives define mineral and compare the two main groups identify the six types of silicate...
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Objectives• Define mineral and Compare the two main groups
• Identify the six types of silicate crystalline structures.
• Describe three common nonsilicate crystalline structures.
• Describe seven physical properties that help distinguish one mineral from another.
• List five special properties that may help identify certain minerals.
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Mineral Identification Basics• Mineral: neral: a solid with an orderly a solid with an orderly
internal structureinternal structure
• To be a mineral, a substance To be a mineral, a substance must have must have 4 characteristics:4 characteristics:
1.1. must be inorganicmust be inorganic—not —not made of living thingsmade of living things
2.2. must occur naturallymust occur naturally——not man-madenot man-made
3.3. must be a crystalline must be a crystalline solidsolid
4.4. must have a consistent must have a consistent chemical compositionchemical composition
Cubic Fluorite Crystal
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Characteristics of Minerals
The diagram below shows the 4 characteristics of minerals
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Silicate Minerals• All minerals can be classified
into two main groups—silicate minerals and nonsilicate minerals
• Silicate mineral: a mineral which contains silicon and oxygen, and may contain one or more metals– Common silicate minerals
include quartz, feldspars, and micas
– Silicate minerals make up 96% of Earth’s crust. Quartz and feldspar alone make up more than 50% of the crust.
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Nonsilicate Minerals• Nonsilicate mineral: a
mineral that does not contain silicon and oxygen– comprise about 4% of
Earth’s crust– organized into six major
groups.
1. Carbonates2. Halides3. native elements4. Oxides5. Sulfates6. sulfides
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Crystalline Structure• Crystal: a solid whose
atoms, or molecules are arranged in a regular, repeating pattern
• Each mineral has a specific geometric arrangement of atoms, also known as its crystalline structure.
• Scientists study the structure of crystals using X rays. These produce an image which shows the geometric arrangement of atoms in the crystal.
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Physical Properties of Minerals• Mineralogist: a person who
examines, analyzes, and classifies minerals
• Each mineral has specific properties, which are the result of its composition and crystalline structure. These properties provide useful clues for identifying minerals.
• The 6 properties used to classify minerals are:
1. Color2. Streak3. Luster4. Cleavage5. Fracture6. Hardness
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Color
• Color: most noticeable property, but least-accurate method for identifying a mineral
Many minerals have similar colors
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Streak
• Streak: color of a mineral in powdered form• More reliable than color
for mineral identification• Determined by rubbing
the mineral against a streak plate
• The streak is often different from the apparent color of an unground sample
• The streak color of a mineral will always be the same, even it its external color varies
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Most metallic minerals have a dark streak
Magnetite
Galena
Chalcopyrite and Galena
Graphite
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…while most nonmetals have a light streak
calcite
Peridot (polished)
Amethyst
Citrine
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Luster
• Luster: The quality and intensity of light reflected from the surface of a mineral
• Luster is either metallic or nonmetallic
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Metallic Luster• Metal-like shine• Dark Streak
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Nonmetallic Luster
• More common• Light streak color
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Cleavage and Fracture• Cleavage: tendency of a mineral
to split• Occurs due to weakness in structure
of mineral
• Fracture: the way a mineral breaks along either curved, or irregular surfaces
• Uneven or irregular fractures have rough surfaces.
• Curved fractures are smooth
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Hardness• Hardness: measure of
resistance to scratching
• A harder substance will scratch a softer substance
• Hardness can be determined by comparing the mineral to those on the Mohs hardness scale ->
Mohs Hardness Scale
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Magnetism
•Magnetism: ability of a mineral to act as a magnet
•Most commonly associated with minerals rich in iron
•Minerals rich in iron are called magnetites
•Iron is highly magnetic…remember this!
This is a piece of iron with a magnet attached
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Magnetism
This is a sample of “black sand” from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper?
This technique is used to separate out much of the unwanted material in the search for gold.
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Magnetism
Lodestone is a variety of Magnetite which is a
natural magnet.
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Fluorescence
• A few minerals have some additional, special properties
• The ability to glow under ultraviolet light is called fluorescence.
• Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.
Willemite