Mineralogy Basics

Definition of Minerals

• Minerals are naturally occurring inorganic elements or compounds.
• They possess a definite chemical composition and orderly internal structure.
• Distinction from rocks: unlike rocks, minerals cannot be decomposed into smaller units with different chemical compositions.

Physical Properties of Minerals

• Luster: Refers to the reflection of light off a mineral's surface.
• Hardness: A measure of a mineral's resistance to scratching, developed in the Mohs scale by Friedrich Mohs over 100 years ago.
  • Mohs hardness scale ranges from 1 (talc) to 10 (diamond).
  • Talc is the softest mineral; diamond is the hardest, capable of scratching all substances.

Mohs Hardness Scale

• Talc: 1, easily scratched by a fingernail; used in talcum powder.
• Gypsum: 2, can be scratched by a fingernail; ingredient in plaster.
• Calcite: 3, scratched by a copper penny; used in cement.
• Fluorite: 4, scratched by a steel nail; used in toothpaste.
• Apatite: 5, scratchable by a steel nail; found in bone.
• Feldspar: 6, can scratch glass; used in glass-making.
• Quartz: 7, can scratch steel and glass; used in glass and electronics.
• Topaz: 8, can scratch quartz; a gemstone.
• Corundum: 9, includes rubies and sapphires; scratchable by very hard materials.
• Diamond: 10, the hardest mineral.

Crystal Form and Habit

• Represents the characteristic shapes of mineral units, whether individual crystals or groups.

Color and Streak

• Color: Often the most visible characteristic but least diagnostic due to variations.
• Streak: The powdered form color of the mineral, useful for identifying minerals. Hematite, for example, produces a reddish-brown streak.

Cleavage and Fracture

• Cleavage: The ability of a mineral to break along preferred planes; can have 1 to 6 cleavage planes.
• Fracture: Irregular breakage of a mineral, unlike cleavage.

Specific Gravity

• Reflects the "heaviness" of a mineral, calculated as the ratio of the mineral's weight to the weight of an equal volume of water (water has a specific gravity of 1).

Other Identifying Properties

• Magnetism: Some minerals like magnetite are strongly magnetic.
• Odor and Taste: Sulfur has a distinctive smell; halite is salty.
• Reaction to Acid: Calcite fizzes with acid.
• Tenacity: Describes toughness:
  • Fragile: Easily broken (e.g., sulfur).
  • Malleable: Can be flattened into sheets (e.g., gold).
  • Ductile: Can be drawn into wires (e.g., copper).
  • Sectile: Can be cut into shavings (e.g., gypsum).
  • Flexible: Can be bent without breaking (e.g., molybdenite).
  • Elastic: Returns to original shape after bending (e.g., micas).

Classification of Minerals

• Based on chemical composition:
  • Metals: e.g., chromium
  • Non-metals: e.g., diamond, graphite
  • Metalloids: e.g., brass, iron-nickel
• Native Elements: Comprised of single elements bonded to themselves.

Examples of Mineral Classes

• Carbonates: e.g., calcite (CaCO3), cerussite (PbCO3).
• Nitrates: e.g., niter (KNO3).
• Phosphates: e.g., apatite.
• Oxides: e.g., hematite (Fe2O3).
• Sulfates: e.g., barite.
• Sulfides: e.g., pyrite.

Common Rock-Forming Minerals

• Minerals with noteworthy physical and chemical properties used in geological studies and applications.