⛏️Intro to Geology Unit 2 – Minerals: The Foundation of Rocks

What Are Minerals?

• Naturally occurring inorganic solids with a definite chemical composition and ordered atomic structure
• Composed of one or more elements (gold, copper) or compounds (quartz, mica)
• Form through various geological processes such as crystallization from magma, precipitation from water, or metamorphism
• Essential building blocks of rocks and play a vital role in the Earth's crust and mantle
• Exhibit unique physical and chemical properties determined by their composition and structure
• Can occur in various forms, from small grains to large crystals (amethyst geodes)
• Provide valuable resources for human use, including metals, building materials, and gemstones

Types of Minerals

• Silicates most abundant mineral group, containing silicon and oxygen (olivine, pyroxene, amphibole, mica, feldspar, quartz)
  • Framework silicates have a three-dimensional structure (quartz, feldspar)
  • Sheet silicates form layered structures (mica, clay minerals)
  • Chain silicates have single or double chains of silica tetrahedra (pyroxene, amphibole)
• Carbonates contain the carbonate ion (CO3) (calcite, dolomite)
• Oxides composed of metal cations bonded to oxygen anions (hematite, magnetite, corundum)
• Sulfides formed by the combination of metal cations with sulfur anions (pyrite, galena, sphalerite)
• Native elements occur in their pure form without combining with other elements (gold, silver, copper, sulfur, diamond)
• Halides characterized by the presence of halogen anions (fluorite, halite)
• Sulfates contain the sulfate ion (SO4) (gypsum, anhydrite, barite)

Mineral Properties and Identification

• Color caused by the absorption of specific wavelengths of light due to the presence of certain elements or impurities
• Streak the color of a mineral in powdered form, obtained by rubbing the mineral against a streak plate (hematite has a reddish-brown streak)
• Luster describes the way a mineral reflects light (metallic, vitreous, pearly, silky, dull)
• Hardness resistance to scratching, measured using the Mohs scale (talc has a hardness of 1, while diamond has a hardness of 10)
• Cleavage the tendency of a mineral to break along specific planes of weakness (mica has perfect cleavage, while quartz has no cleavage)
• Fracture the pattern of breakage when a mineral does not have cleavage (conchoidal, uneven, splintery)
• Specific gravity the ratio of a mineral's density to the density of water (gold has a high specific gravity of 19.3)
• Other properties include magnetism (magnetite), taste (halite), and reaction with acid (calcite)

Crystal Structures and Systems

• Crystals are solid materials with a regular, repeating arrangement of atoms or ions
• Crystal structure refers to the specific geometric arrangement of atoms or ions within a crystal
• Unit cell the smallest repeating unit that defines the crystal structure
• Seven crystal systems based on the symmetry and angles of the unit cell (cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, triclinic)
  • Cubic system has equal lengths and 90-degree angles between all axes (pyrite, halite)
  • Hexagonal system has two equal horizontal axes and one unique vertical axis (quartz, beryl)
• Bravais lattices the 14 unique arrangements of points in three-dimensional space that describe all possible crystal structures
• Miller Indices a notation system used to describe the orientation of crystal faces and planes
• Polymorphism the ability of a mineral to have different crystal structures while maintaining the same chemical composition (diamond and graphite are polymorphs of carbon)

Formation of Minerals

• Crystallization from magma minerals form as magma cools and solidifies (olivine, pyroxene, feldspar)
  • Bowen's reaction series describes the order in which minerals crystallize from magma based on their temperature and composition
• Precipitation from aqueous solutions minerals precipitate when the solution becomes supersaturated (halite, gypsum)
  • Evaporite deposits form in arid environments where water evaporates, leaving behind concentrated mineral deposits (Bonneville Salt Flats)
• Hydrothermal processes minerals form from hot, mineral-rich fluids circulating through rocks (quartz veins, sulfide deposits)
• Metamorphism minerals recrystallize or form new minerals under high temperature and pressure conditions (garnet, kyanite)
• Weathering and alteration minerals can form through the breakdown or alteration of pre-existing minerals due to exposure to air, water, or biological activity (clay minerals, limonite)
• Biogenic processes minerals are formed by living organisms (calcium carbonate in shells, silica in diatoms)

Economic Importance of Minerals

• Ore deposits concentrated accumulations of economically valuable minerals (copper porphyry deposits, gold veins)
• Metallic minerals sources of valuable metals such as iron, copper, aluminum, and precious metals (hematite, chalcopyrite, bauxite, gold)
• Industrial minerals used in construction, manufacturing, and agriculture (gypsum for drywall, quartz for glass, phosphates for fertilizers)
• Gemstones highly prized for their beauty, rarity, and durability (diamond, ruby, sapphire, emerald)
• Energy resources minerals used in the production of energy (coal, uranium)
• Technology and innovation minerals are essential components in advanced technologies (rare earth elements for magnets and electronics)
• Environmental concerns mining and processing of minerals can have significant environmental impacts (acid mine drainage, habitat destruction)
• Sustainable resource management balancing the economic benefits of mineral extraction with environmental and social responsibility

Minerals in Rock Formation

• Igneous rocks form from the cooling and solidification of magma or lava
  • Intrusive igneous rocks crystallize slowly beneath the Earth's surface (granite, diorite, gabbro)
  • Extrusive igneous rocks form when lava cools rapidly on the Earth's surface (basalt, rhyolite, obsidian)
• Sedimentary rocks form through the deposition and lithification of sediments
  • Clastic sedimentary rocks composed of rock and mineral fragments (sandstone, conglomerate, shale)
  • Chemical sedimentary rocks form by precipitation from aqueous solutions (limestone, chert, rock salt)
• Metamorphic rocks form when pre-existing rocks are subjected to high temperature and pressure
  • Foliated metamorphic rocks have a layered or banded appearance (gneiss, schist, slate)
  • Non-foliated metamorphic rocks have a more uniform texture (marble, quartzite)
• Minerals as indicators of rock formation conditions (index minerals) can provide information about the temperature, pressure, and chemical environment during rock formation

Lab Skills and Field Techniques

• Mineral identification using physical properties (color, streak, luster, hardness, cleavage, fracture, specific gravity)
• Optical mineralogy using polarized light microscopy to study the optical properties of minerals in thin sections
• X-ray diffraction (XRD) analysis determining the crystal structure and composition of minerals using X-ray scattering
• Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) for high-resolution imaging and chemical analysis of mineral surfaces
• Geochemical analysis using techniques such as inductively coupled plasma mass spectrometry (ICP-MS) to determine the elemental composition of minerals
• Field observations and sampling collecting and documenting mineral specimens in their natural geological context
• Geological mapping plotting the distribution and relationships of minerals and rocks in a given area
• Remote sensing using satellite imagery and geophysical data to identify mineral deposits and map geological structures