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Objective
3 Define chemical and physical properties of minerals to include luster, hardness, cleavage, fracture, streak, color, specific gravity, and special traits.
Enduring Understanding
• Minerals are the building blocks of rocks.
Mineral Identification
• With more than 3,000 minerals in Earth’s crust how does one go about identifying an unknown mineral?
Mineral Identification
• Geologists rely on several simple tests that are based on a mineral’s physical and chemical properties. It is usually best to use a combination of tests rather than just one to identify minerals
Mineral Properties
• Color is one of the most noticeable but least reliable characteristics
Mineral Properties
• Sometimes caused by the presence of trace elements or compounds
Mineral Properties
• Streak is the color of the mineral when it is broken up into a powder and is a much more reliable identification method because it rarely changes
Both of these samples are hematite; both have a reddish-brown streak
Mineral Properties
• Streak is easily determined by rubbing the mineral across an unglazed porcelain plate
Mineral Properties
• Streak is used to distinguish pyrite from gold
Mineral Properties
• Streak is used to distinguish pyrite from gold
Mineral Properties
• Luster is the way a mineral reflects light from its surface and is caused by differences in mineral chemical compositions
Mineral Properties
• Either metallic or nonmetallic (dull, pearly, waxy, silky)
Mineral Properties
• Texture describes how a mineral feels to the touch– Rough, smooth, ragged, greasy, soapy, glassy
Mineral Properties
• Hardness is a measure of how easily a mineral can be scratched and is determined by the arrangement of it’s atoms.
Mineral Properties
• The Mohs hardness scale is used to compare a sample to the hardness of ten known minerals
Mineral Properties
• Cleavage determines whether a mineral will split easily and evenly along one or more flat planes
Mineral Properties
• Mica has perfect cleavage in one direction
• Halite has cubic cleavage (3 planes)
Mineral Properties
• Fracture means the mineral is tightly bonded and breaks with rough or jagged edges– Quartz has fracture
Mineral Properties
• Specific Gravity compares the weight of the mineral to an equal volume of water at 4 degrees C
Mineral Properties
• Special Properties such as light reflection and reactions to acids are also useful tools
Mineral Properties
• Calcite fizzles when in contact with HCl
Mineral Properties
• Calcite also can cause double images
Mineral Properties
• Magnetite will attract iron
Mineral Properties
• Sulfur produces a rotten egg odor
MINERALS GENERAL NOTES
Minerals
•Minerals have four characteristics
4
Naturally occurring—formed by processes on or inside Earth with no input from humans
Living
Inorganic—not made by life processes
Element or compound with a definite chemical composition
Orderly arrangement of atoms; all minerals are crystalline solids
Crystal—solid with atoms arranged in orderly, repeating patterns
Some crystals form from magma, hot melted rock below the Earth’s surface.
When magma cools slowly, crystals are large.
When magma cools quickly, crystals are small.
Crystals can form from solutions as water evaporates or if too much of a substance is dissolved in water.
• Mineral groups are defined by their composition.
• Silicates contain silicon, oxygen, and one or more other elements; they include most common rock-forming minerals.
• Silicon and oxygen are the two most abundant elements in Earth’s crust; they form the building blocks of many minerals.
DISCUSSION QUESTION:• What processes can cause crystals to form?
DISCUSSION QUESTION:• What processes can cause crystals to form? Crystals form from cooling magma, from
evaporating solutions, and from solutions in which too much of a substance is dissolved.
Mineral Identification
• Color and appearance are not enough to distinguish most minerals.
• Hardness is a measure of how easily a mineral can be scratched; the Moh’s scale compares mineral hardness.
1. Talc - easily scratched by the fingernail 2. Gypsum - just scratched by the fingernail 3. Calcite - scratches and is scratched by a copper coin 4. Fluorite - not scratched by a copper coin and does not
scratch glass 5. Apatite - just scratches glass and is easily scratched by a
knife 6. Orthoclase - easily scratches glass and is just scratched by a
file 7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not
scratched by a file 8. Topaz - scratched only by corundum and diamond 9. Corundum - (sapphires and rubies) scratched only by a
diamond 10.Diamond - scratched only by another diamond
• The way a mineral reflects light is its luster.• Luster can be metallic or nonmetallic
• Nonmetallic lusters include dull, pearly, silky, and glassy.
Specific gravity is the relationship between a mineral’s density to the density of water. If the specific gravity is larger than one it will sink in water, if it is smaller than one it will float in water.
Streak is the color of a mineral in powdered form, but the streak test is useful only for minerals softer than the streak plate.
The way a mineral breaks can be a distinguishing characteristic.
Minerals with cleavage break along smooth, flat surfaces.
Minerals with fracture break with uneven, rough, or jagged surfaces.
Some minerals have unique properties that involve light or magnetism.
DISCUSSION QUESTION:• What are five properties that could be
examined to identify a mineral?
DISCUSSION QUESTION:• What are five properties that could be
examined to identify a mineral? hardness, luster, specific gravity, streak,
cleavage, and fracture
Gems—rare and beautiful minerals that are highly prized
The Cullinan diamond and the Hope diamond are famous historical gems.
Gems have industrial applications in abrasives, lasers, and electronics.
Minerals can contain other useful elements.
An ore is a mineral or rock containing a substance that can be mined at a profit.
Elements must be refined, or purified, from ores.
• Some elements dissolve in fluids, travel through weaknesses in rocks, and in those weaknesses form mineral deposits called vein mineral deposits.
Titanium is a useful element derived from the minerals ilmenite and rutile.
Mica is an example of a mineral with the characteristic of cleavage, because it can be separated into sheets.
Graphite is one of the softest minerals and is used in pencils.
Sulfur is a bright yellow mineral with the distinctive odor of spoiled eggs.
Calcite is a hard carbonate mineral
Feldspar is the most abundant mineral in the Earth's crust
Hematite is an iron based mineral, colored black, silver-gray, reddish brown, or red.
Halite – the mineral sodium chloride also known as table salt
