Minerals & Rocks Quiz

Definition of a Mineral

• Minerals are naturally occurring, inorganic solids with a definite chemical composition and crystal structure.
• Examples include graphite (used in pencils and batteries), sulfur (found in matches and fireworks), and talc (used in powder and ceramics).
• Man-made substances (e.g., cement, steel) do not qualify as minerals.

Non-Silicate Subdivisions

• Native Elements: Minerals occurring in nature in their pure elemental form, such as gold (Au), sulfur (S), and silver (Ag).
• Sulfides: Contain sulfur ions; notable examples are galena (PbS) and pyrite (FeS2).
• Sulfates: Contain the sulfate ion ($SO_4^{2-}$), such as gypsum ($CaSO_4.2H_2O$).
• Oxides: Minerals with oxygen bonded to metals, including hematite ($Fe_2O_3$) and magnetite ($Fe_3O_4$).
• Halides: Comprise minerals with halogen ions like fluorine or chlorine, e.g., halite ($NaCl$) and fluorite ($CaF_2$).
• Carbonates: Contain the carbonate ion ($CO_3^{2-}$), with calcite ($CaCO_3$) and dolomite ($CaMg(CO_3)_2$) as common examples.

Crystal Structure

• Refers to the arrangement of atoms in a mineral; organized in repeating geometric patterns.
• Six Basic Crystal Systems:
  • Cubic: Galena, halite, pyrite
  • Tetragonal: Chalcopyrite
  • Hexagonal: Quartz, calcite
  • Orthorhombic: Olivine, topaz
  • Monoclinic: Mica, gypsum
  • Triclinic: Feldspar, turquoise

Physical Properties

• Hardness: Measured by scratchability; defined through Mohs Hardness Scale, ranking minerals from talc (1) to diamond (10).
• Cleavage: Describes how a mineral splits along flat surfaces; examples include mica (one direction) and galena (three directions).
• Color: Can be varied and is influenced by impurities and environmental exposure; not always reliable for identification.
• Streak: The color of a mineral in powdered form, useful for identification (e.g., quartz leaves white streak, hematite leaves reddish-brown).
• Luster: Describes how minerals reflect light; categories include metallic (galena) and non-metallic (quartz).

Mineral Formation

• Minerals can form through cooling of magma/lava, evaporation of water, or supersaturation leading to precipitation.

Identifying Minerals

• Identification relies on physical properties such as color, streak, luster, hardness, cleavage, fracture, and density, as well as chemical properties that reflect the mineral's composition and structure.

Chemical Properties

• Effervescence: Observable reaction with acid (e.g., calcite reacts with HCl, producing bubbles of CO2).
• Oxidation:
  • Iron rusts when reacting with oxygen, weakening the metal.
  • Copper reacts with air to form a non-damaging greenish oxide, commonly seen on pennies.

Fracture and Density

• Fracture: Irregular breakage of minerals resulting in jagged surfaces; seen in minerals like sulfur and quartz.
• Density: The weight of a mineral for a given volume, perceived as heaviness when held.