Mineral Characteristics and Identification

Mineral Characteristics

• Minerals are naturally occurring, inorganic solids.
• They have a specific chemical composition.
• They have a definite crystalline structure.
• Minerals are solids.
• Most minerals are made from compounds.
• Crystals are solids in which atoms are arranged in repeating patterns.

Examples of Minerals

• Olivine
• Augite
• Hornblende
• Biotite
• Calcium-rich plagioclase (anorthite)
• Sodium-rich plagioclase (albite)
• Potassium-rich feldspar (commonly orthoclase)
• Muscovite
• Quartz
• Calcite

How Minerals are Formed

• Solutions: Minerals can form from the evaporation of dissolved liquids (evaporites).
• Magma: Molten material below Earth's surface is called magma. Small crystals form from rapidly cooling magma; large crystals form from slowly cooling magma.

Identifying Minerals

• Color: While noticeable, color is not always a reliable identifier.
• Luster: The way a mineral reflects light.
• Streak: The color of a mineral's powder when broken up.
• Cleavage/Fracture: Describes how a mineral breaks (evenly along planes vs. rough/jagged edges)
• Hardness: A measure of how easily a mineral can be scratched.
• Crystal Shape: Some minerals have distinctive crystal shapes that help with identification.
• Special Properties: Some minerals have unique properties like magnetism, iridescence, or fluorescence that can be used to identify them.

Rock-Forming Minerals

• Rock-forming minerals are primarily made up of the eight most common elements in Earth's crust (Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium).
• Quartz, feldspar, amphibole, olivine, mica, pyroxene, garnet, and calcite are the most common rock-forming minerals.
• About 8-10 of these minerals make up most of the rocks in Earth's crust.

Types of Minerals

• Silicates: Minerals containing silicon and oxygen, making up roughly 96% of Earth's crustal minerals.
• Carbonates: Minerals composed of metallic elements and the carbonate ion (CO32-). Magma, being less dense, rises through surrounding rock to cool and crystallize in Earth's crustal interior.
• Oxides: Compounds of oxygen and a metal (e.g., hematite (Fe₂O₃)).
• Sulfides: Compounds of sulfur and one or more elements (e.g., pyrite (FeS₂)).
• Sulfates: Compounds containing the sulfate ion (SO₄²⁻) (e.g., anhydrite (CaSO₄)).
• Halides: Minerals made of chloride or fluoride combined with calcium, sodium, or potassium (e.g., halite (NaCl)).
• Native Elements: Minerals made of a single element (e.g., silver (Ag)).

Economic Minerals

• Some minerals are used in various products such as computers, cars, etc.
• Ore: A mineral that contains a useful substance that can be mined profitably.
• Gems: Valueable minerals prized for their rarity and beauty.