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.

Test your knowledge about the defining qualities of minerals. This quiz covers the characteristics that classify materials as minerals, methods to test for them, and examples of various minerals. Explore the fascinating world of geology and discover what makes a mineral unique.