Mineral Identification

Changes: Subscripts/superscripts formated (1/30/04)

Physical Properties

• Crystal habit - well formed, not well formed
• Hardness
• related to size, charge, and packing
• Mohs Hardness Scale
• 1. talc
• 2. gypsum
• 3. calcite
• 4. fluorite
• 5. apatite
• 6. orthoclase
• 7. quartz
• 8. topaz
• 9. corundum (ruby, sapphire)
• 10. diamond

• Cleavage
• Tendency to break along a plane of weakness
• Cleavage direction - 1, 2, 3?
• 1: mica (e.g., biotite)
• 2: pyroxene
• 3: halite, calcite
• Cleavage quality
• Poor to excellent (e.g., mica)
• Fracture -
• Characteristic breakage pattern
• Conchoidal , fibrous, splintery, etc.

Mineral Identification (cont.)
Physical and Other Properties

• Luster - vitreous, pearly, metallic, etc.
• Color (including streak)
• Specific gravity and density
• Chemical Properties
• acid test - calcite, dolomite(?)
• Optical properties - petrographic microscope
• Atomic spacing - x-ray diffraction (best)

Mineral (Supplemental)

• Crystals versus crystalline solid
• Crystals have orderly atomic structure and crystal faces
• Crystalline solid has orderly atomic structure but may not have space to form crystal faces
• Crystal habit
• Well formed, not well formed
• In well formed crystals, angle between crystal faces

Ex. quartz--6-sided, halite--cubic, calcite--rhombohedral

Mineral Classification

• Eight common crustal elements as ions:

O^2-, Si⁴⁺, Al³⁺, Fe^2+,3+ ,Ca²⁺, Mg²⁺, Na⁺, K⁺

• Nine rock-forming minerals:

olivine, pyroxene, amphibole, mica, clay minerals, feldspar, quartz, calcite, dolomite

• Accessory minerals - common but in small amounts; often diagnostic of origin of rock
• e.g., chlorite, garnet, hematite, pyrite

• Classified based on anion
• Silicates - SiO₄^4- anion
• Silicon-oxygen tetrahedron - building block; interconnected or bonded by cations
• Isolated - olivine1 (Fe, Mg)₂SiO₄
• Ring - beryl
• Chain
• single - pyroxene (Fe, Mg)SiO₃
• double - hornblende (amphibole); hydrous Fe, Mg silicate
• Sheet - biotite (mica), clay minerals
• Framework
• Quartz - SiO₂
• Feldspars - orthoclase (KAlSi₃O₈), plagioclase (CaAl₂Si₂O₈ –> NaAlSi₃O₈ )

• Chemical Trends
• Isolated - olivine
• Ring - beryl
• Chain-- pyroxene, amphibole
• Sheet - mica, clay minerals
• Framework - quartz, feldspars

Rock-Forming Minerals
Classification (cont.)

• Non-silicates
• Native elements - gold, silver, sulfur, carbon (polymorphs graphite and diamond)
• Carbonates (CO₃ ^2-) 
• Polymorphs calcite and aragonite - CaCO ₃
• Dolomite - CaMg(CO₃ )₂
• Oxides (O^2- ) - hematite (Fe₂O ₃), spinel (Mg₂ Al₂O ₄)
• Sulfides (S^2- ) - pyrite (FeS₂)
• Sulfates (SO ₄^2-)
• Anhydrite (CaSO ₄)
• Gypsum (CaSO₄ • 2H ₂O) - hydrated

Rock Mineralogy

• Function of origin