Minerals – Key Points

Mineral Definition

• Minerals = building blocks of rocks.
• Criteria (must satisfy ALL):
  • Naturally occurring (formed by Earth processes, not man-made).
  • Inorganic (no carbon from living organisms; e.g., coal ≠ mineral).
  • Homogeneous solid (uniform appearance; stable at room T).
  • Definite chemical composition (fixed or limited range formula; e.g., $\text{SiO}_2$).
  • Orderly crystalline structure (atoms arranged in repeating 3-D pattern).

Mineral Formation

• Cooling of magma/lava ➔ crystal growth.
  • Slow cooling ➔ large crystals.
  • Fast cooling ➔ small crystals.
• Evaporation of mineral-rich water ➔ precipitation of crystals.

Mineral vs. Not Mineral (examples)

• Minerals: Talc, Fluorite, Galena, Quartz, Pyrite.
• Not Minerals: Crude Oil, Coal.

Physical Properties for Identification

• Color: visible hue; unreliable due to impurities.
• Streak: color of powdered mineral.
• Luster: reflection of light.
  • Metallic vs. Non-metallic (pearly, waxy, vitreous, silky, etc.).
• Hardness: resistance to scratching; measured by Mohs scale.
• Cleavage: breaks along flat planes.
• Fracture: irregular breakage.
• Tenacity: response to stress.
  • Brittle, malleable, ductile, flexible-inelastic, flexible-elastic, sectile.

Mohs Hardness Scale (reference values)

• Diamond $10$
• Corundum $9$
• Topaz $8$
• Quartz $7$
• Orthoclase $6$
• Apatite $5$
• Fluorite $4$
• Calcite $3$
• Gypsum $2$
• Talc $1$

Quick Recall

• “Hardness” = resistance to scratching.
• Minerals = naturally occurring, inorganic, solid, definite composition, crystalline.
• Streak test distinguishes minerals with similar external color (e.g., hematite $\rightarrow$ reddish streak).
• Cleavage vs. Fracture: flat vs. irregular break surfaces.
• Historical gold test (bite mark) checked for sectility/softness, relating to hardness.