Minerals

Minerals What is a mineral? What is a rock? Naturally occurring Crystalline solid Inorganic Specific chemical composition Definite structure What is a rock? Composed of one or more minerals

Mineral Formation Minerals form from: Cooling magma Precipitation from water

Minerals There are 4500 known minerals ~200 are common ~24 form the majority of rocks Minerals form under specific heat and pressure conditions Minerals are used to classify and interpret rocks

Properties of Minerals Seven important characteristics for identifying minerals Luster Color (sometimes ambiguous) Streak Hardness Crystal habit Breakage (Fracture or Cleavage) Specific Gravity

Properties of Matter – Crystal Habit The external shape Mineral crystals occur in various shapes and sizes Shape is determined by the arrangements of the atoms, molecules or ions that make up the crystal and how they are joined

Properties of Minerals --Hardness Measure of resistance to scratching Hard mineral = very resistant to scratching Measured on Moh’s hardness scale

Properties of Minerals -- Color NOT always a good diagnostic property – can be misleading Most minerals have a wide range of colors Example: Quartz Color is the result of impurities A few minerals DO have characteristic colors Ex. Olivine is always green

Properties of Minerals – Streak The color of powdered mineral COLOR may vary, but streak is usually the same Hematite always has a red streak (whether it has an earthy or metallic luster)

Properties of Minerals -- Luster The way light reflects off surface Metallic Nonmetallic Earthy Glassy Pearly Greasy

Properties of Minerals – Specific Gravity Ratio of mineral mass to mass of an equal volume of water How HEAVY does the mineral feel? Galena is a heavy mineral

Properties of Minerals – Breakage Cleavage: Break along zones of weakness in crystal lattice Tendency of a mineral to break along planes of weak bonds Creates smooth, parallel surfaces

Properties of Minerals -- Breakage Fracture: uneven break when no weak zones exist Mineral has strong bonds in all directions Breaks along uneven, irregular surfaces OR Breaks along curved, conchoidal surface

Special Properties Magnetism Taste Reaction to HCl Fluorescence Magnetite Taste Halite tastes salty Reaction to HCl Calcite reacts to HCl Fluorescence Fluorite, Calcite

Economic Minerals Ores A mineral that contains a valuable substance that can be mined at a profit Classification can change is the mineral’s supply and demand lowers (may no longer be considered an ore) Example: iron found in the mineral hematite

Economic Minerals Gemstones Gemstones are minerals that are valuable due to their rarity and beauty Pure, Very little defects Rare Transparent Even coloration Hardness >7 (not easily scratched)

Gemstones Sapphires and rubies are both corundum (Al2O3) Sapphires blue are due to titanium and iron Rubies are red due to chromium Because of their rareness, rubies and emeralds are more valuable than diamonds