Matter and Minerals - Quick Reference (Focus Questions 1.1–1.5)

Focus Question 1.1

  • Naturally occurring

  • Inorganic solid

  • Orderly crystalline structure

  • Definite chemical composition

  • Minerals are building blocks of rocks; composition may vary slightly via substitution but crystal structure remains: example \mathrm{SiO_2} for quartz

Focus Question 1.2

  • Atoms are built from:

    • Protons (charge +1) in the nucleus

    • Neutrons (charge 0) in the nucleus

    • Electrons (charge -1) in the electron cloud

  • Nucleus + electron cloud; atomic number = number of protons; defines the element

  • ~90 naturally occurring elements; arranged in the periodic table

  • Atom: the smallest unit that cannot be chemically split

  • Valence electrons in the outer shell interact to form bonds

  • Atoms comprise various subatomic particles: protons, neutrons, electrons

Focus Question 1.3

  • Atoms bond to lower total energy and become more stable

  • Octet Rule: atoms tend to have 8 valence electrons in their outer shell

  • Bond types:

    • Ionic bonds: electrons transferred; oppositely charged ions attract

    • Covalent bonds: electrons are shared

    • Metallic bonds: valence electrons move freely between atoms

  • Example: NaCl forms via transfer of one electron from Na to Cl producing Na$^+$ and Cl$^-$

Focus Question 1.4

  • Physical properties used to identify minerals:

    • Luster: metallic, submetallic, nonmetallic (vitreous/glassy, dull, earthy, pearly, silky, greasy)

    • Transparency: opaque, translucent, transparent

    • Color vs. streak: streak (color of powdered mineral) is more diagnostic than color

    • Crystal habit (shape) and crystal form

    • Tenacity: brittle, malleable, sectile, elastic

    • Hardness: Mohs scale 1\le H\le 10; reference values: talc 1, gypsum 2, calcite 3, copper penny 3.5, glass 5.5, quartz 7, diamond 10

    • Cleavage: break along planes of weak bonding; directions and angles (examples below)

    • Fracture: irregular or conchoidal

    • Density / Specific gravity: ratio of mineral weight to equal volume of water; typical SG\sim 2-3; metals often higher (e.g., gold ~ 20)

    • Other properties: taste (halite), feel (talc = soapy; graphite = greasy), smell (sulfur), magnetism, optical properties, effervescence with acid

  • Cleavage examples:

    • Muscovite: one direction

    • Feldspar: two directions at 90^
      0^a0\circ

    • Hornblende: two directions at 60^\u0000a0\circ and 120^
      0\circ

    • Halite: three directions at 90^
      0\circ

    • Calcite: three directions not at 90^
      0\circ

    • Fluorite: four directions

  • Note on bonds: cleavage is about weak bonding planes; fracture is about bond strength across the mineral

Focus Question 1.5

  • Mineral groups:

    • Silicates (most abundant): based on silicon-oxygen tetrahedron; >800 silicate minerals; ~90% of Earth’s crust; feldspars are most abundant; quartz is the second most abundant; silicate structures form chains, sheets, and three-dimensional networks

    • Silicate structures:

    • Single tetrahedra (Olive) — Olivine group

    • Single chains — Pyroxene group

    • Double chains — Amphibole group

    • Sheets — Micas (Biotite, Muscovite)

    • Three-dimensional networks — Feldspar and Quartz

    • Light silicates: Feldspars (Orthoclase, Plagioclase), Quartz, Muscovite, Clay minerals

    • Dark silicates: Olivine, Pyroxenes, Amphiboles, Biotite, Garnet

  • Nonsilicate minerals (≈8% of crust):

    • Carbonates: Calcite, Dolomite

    • Halite, Gypsum

    • Oxides: Hematite, Magnetite

    • Sulfides: Galena, Sphalerite

    • Native elements: Gold, Silver, Copper

    • Fluorite, Corundum, Uraninite

  • Summary: Silicates dominate crust chemistry; non-silicates provide many economically important minerals; rock-forming minerals are primarily silicates.