Minerals

Definition and characteristics: Definition: To be a mineral, a substance must be: - Naturally occurring (not synthetic) - Inorganic (not formed by biological processes, with a few exceptions like shells) - Solid (not liquid or gas at standard conditions) - Have a definite chemical composition (can be written as a formula) - Have an ordered atomic structure (crystalline) Crystalline Structure: Atoms are arranged in a repeating, three-dimensional pattern. This gives minerals their characteristic properties and crystal forms. Chemical Composition: Each mineral has a specific chemical formula. Some allow substitutions (solid solution), but composition is within defined limits. Physical Properties: Result from chemical composition and crystal structure: - Hardness, cleavage, color, luster, specific gravity, and many others - These properties help identify minerals Mineral vs. Rock: Minerals are the building blocks. Rocks are aggregates of one or more minerals. A single mineral can be a rock (like quartzite, which is mostly quartz). Number of Minerals: Over 5,000 minerals are known, but only about 100 are common. Most rocks are composed of just a few common minerals.

How minerals are organized: By Chemical Composition: Minerals are classified into groups based on their dominant anion (negative ion) or anionic group: - Silicates (most abundant) - Carbonates - Oxides - Sulfides - Sulfates - Halides - Native elements - And others Silicates: Most important group, make up about 90% of Earth's crust: - Framework silicates: Quartz, feldspars - Sheet silicates: Micas, clays - Chain silicates: Pyroxenes, amphiboles - And other subclasses Dana Classification: System developed by James Dana, organizes minerals by composition and structure. Still widely used. Crystal System: Minerals are also classified by crystal system (cubic, tetragonal, etc.). This is a secondary classification. Practical Use: Classification helps organize knowledge, predict properties, and identify minerals. Understanding classes helps narrow down identification possibilities.

Minerals that make up most rocks: Quartz (SiO₂): - Most common mineral after feldspars - Very hard (7), no cleavage, many colors - Forms in all rock types - Many varieties: amethyst, citrine, agate, jasper, etc. Feldspars: - Most common mineral group - Two main types: - Potassium feldspar: Orthoclase, microcline - Plagioclase: Range from sodium to calcium end members - Common in igneous and metamorphic rocks Micas: - Sheet silicates with perfect cleavage - Muscovite: Light-colored, common in felsic rocks - Biotite: Dark-colored, common in many rock types Pyroxenes: - Chain silicates, common in mafic rocks - Examples: Augite, diopside - Form prismatic crystals Amphiboles: - Double-chain silicates - Example: Hornblende (common in many rocks) - Similar to pyroxenes but different cleavage angles Olivine: - Common in mafic and ultramafic rocks - Usually green, granular - Gem variety: Peridot Calcite (CaCO₃): - Most common carbonate - Forms limestone and marble - Reacts with acid (effervesces) Clay Minerals: - Fine-grained sheet silicates - Common in sedimentary rocks and soils - Important for many applications

How to identify minerals: Visual Properties: First observations: - Color (can be variable, not always reliable) - Luster (metallic vs. non-metallic) - Crystal form (if visible) - Habit (typical appearance) Physical Tests: - Hardness: Resistance to scratching (Mohs scale 1-10) - Cleavage: How it breaks (number of directions, angles) - Fracture: Conchoidal, uneven, etc. - Streak: Color of powdered mineral - Specific Gravity: Density relative to water Special Properties: - Reaction to acid (carbonates effervesce) - Magnetism (magnetite is magnetic) - Fluorescence (some glow under UV light) - Taste (halite is salty - but don't taste unknown minerals!) Systematic Approach: 1. Observe luster (metallic vs. non-metallic) 2. Test hardness 3. Observe cleavage 4. Test other properties 5. Compare to field guide or database Tools: Basic tools include: - Hardness picks or common objects - Streak plate (unglazed porcelain) - Hand lens (10x loupe) - Field guide or app Practice: Identification improves with practice. Start with common minerals in your area.

How minerals form: Crystallization from Magma: As magma cools, minerals crystallize in a specific order. Different minerals form at different temperatures. Creates igneous rocks and their minerals. Precipitation from Solution: When water becomes supersaturated, minerals precipitate. Forms many sedimentary minerals and creates crystals in veins and geodes. Metamorphic Recrystallization: Existing minerals recrystallize into new forms under heat and pressure. Creates metamorphic rocks and their characteristic minerals. Hydrothermal Deposition: Hot, mineral-rich water deposits minerals as it cools. Creates many ore deposits and beautiful crystal formations. Weathering: New minerals form as rocks weather. Clay minerals, iron oxides, and other secondary minerals are common weathering products. Biological Processes: Some minerals form through biological activity. Shells (calcite, aragonite), some iron minerals, and other biominerals. Time Scales: Mineral formation can be rapid (volcanic crystallization) or very slow (metamorphic recrystallization over millions of years). For Rockhounds: Understanding formation helps predict where to find specific minerals and explains their properties and associations.

Why minerals matter: Ore Minerals: Source of metals and other elements: - Hematite, magnetite: Iron - Chalcopyrite: Copper - Galena: Lead - Bauxite: Aluminum - And many others Industrial Minerals: Used directly or processed: - Quartz: Glass, electronics, many uses - Calcite: Cement, many industrial processes - Gypsum: Plaster, drywall - Talc: Many industrial and consumer products - And many others Gem Minerals: Valued for beauty: - Diamond, corundum (ruby, sapphire), beryl (emerald, aquamarine), and many others - Used in jewelry and decorative arts Building Materials: Many minerals are used in construction: - Calcite (limestone, marble): Building stone, cement - Quartz (sandstone, quartzite): Building stone, glass - Gypsum: Drywall - And many others Scientific Importance: Minerals provide information about: - Earth's composition and history - Formation conditions (temperature, pressure) - Geological processes - Past environments For Rockhounds: Understanding mineral uses helps appreciate the importance of your hobby. Many collected minerals are essential to modern life and have been important throughout human history.