Overview
This lecture covers how to identify common rock-forming minerals using their physical and chemical properties, highlighting key properties and examples of major minerals.
Definition and Criteria of Minerals
- A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and definite chemical composition.
- Water is not a mineral because it is not a solid; tube ice is not a mineral because it is not naturally occurring; snowflakes are minerals.
Physical Properties of Minerals
- Luster: The way light reflects from a mineral's surface; can be metallic (e.g., pyrite) or non-metallic (e.g., kaolinite).
- Hardness: Resistance to scratching, measured by Mohs scale (1 = talc, 10 = diamond), designed by Friedrich Mohs.
- Color: Varies due to impurities and geological processes; e.g., azurite is purple, sulfur is yellow.
- Streak: Color of the mineral in powdered form; more reliable than color; e.g., hematite.
- Crystal Form (Habit): The natural geometric shape a mineral forms before any breakage.
- Cleavage: Tendency to break along flat planes; minerals without cleavage fracture instead, breaking like glass or into fibers.
- Specific Gravity: Ratio of a mineral's density to that of water, measured by water displacement.
Chemical Properties of Minerals
- Chemical tests include odor, taste, and reaction to chemical assays.
- The most stable way to classify minerals is by chemical composition.
- Silicates: Contain silicon and oxygen; over 90% of rock-forming minerals.
- Other mineral classes: oxides, sulfates, sulfides, carbonates, native elements, halides.
Common Rock-Forming Minerals
- Quartz: Composed of silicon dioxide, used to make glass.
- Plagioclase Feldspar: Used in ceramics, important industrial mineral.
- Alkali Feldspar: Pink to white, used for porcelain.
- Micas: Silicates found in igneous and sedimentary rocks.
- Amphiboles: Silicate family, present in igneous and metamorphic rocks.
- Pyroxene: Sometimes used as gemstones.
- Olivine: Clear, can be faceted as gemstones.
- Calcite: Main component of limestone; forms marble through metamorphism.
Key Terms & Definitions
- Luster — How light reflects from a mineral’s surface.
- Hardness — A mineral’s resistance to being scratched.
- Streak — The color of a mineral in powdered form.
- Cleavage — The way a mineral breaks along specific planes.
- Silicates — Minerals containing silicon and oxygen.
Action Items / Next Steps
- Review and memorize the physical and chemical properties of minerals.
- Practice identifying minerals using the listed properties.
- Complete any quiz or worksheet on mineral identification as assigned.