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ROCK - an aggregate of minerals. Examples

• granite (an igneous rock) = quartz, feldspar, mica (minerals)
• limestone (a sedimentary rock) = calcite (a mineral)

MINERAL - a naturally occurring inorganic solid that possesses a definite chemical structure, which gives it a unique set of physical properties. Again,

• must be naturally occurring
• must be inorganic
• must be solid
• must possess a definite chemical structure

(glass, coal, oil, examples of what is not a mineral)

*the earth has about 4000 minerals, but only about a dozen are common rock forming minerals in the earth's crust.

The COMPOSITION and STRUCTURE of a MINERAL is based on the ELEMENTAL PROPERTIES and ARRANGEMENT of ATOMS within a DEFINITE PATTERN or FRAMEWORK.

BASICS OF MINERAL CHEMISTRY

The atomic number (that is the number of PROTONS in the nucleus) and the arrangement of electrons in shells surrounding the nucleus give the atom its electrical charge and atomic size characteristics.

Elements combine in definite proportions to form COMPOUNDS. (MINERALS are COMPOUNDS!) Based on electronic properties of atom, atoms form different kinds of bonds.

• IONIC BONDS - "oppositely charged ions": Examples include salts: CaCO₃, CaSO₄, NaCl (the constituents are found dissolved in seawater).
• COVALENT BONDS - "shared" electrons: more rigid compounds, won't easily dissolve. Examples include,Quartz, - (explains why the beach often consists of quartz sand).
• METALLIC BONDS - "electrical glue,," copper, gold, etc.

ISOTOPES - The MASS NUMBER of an ATOM is total of NEUTRONS and PROTONS. Some ELEMENTS have more than one mass based on variationss in the number of NEUTRONS.

The ATOMIC WEIGHT of an element is based on the average weight of elements in their relative natural abundances. e.g. C¹² and C¹⁴

RADIOACTIVITY is based on the instability of some ISOTOPES. Some isotopes break down to form lighter isotopes or different elements. This is important to the study of radiometric dating. For example, carbon has three isotopes: C¹², C¹³, and C¹⁴. C¹⁴ is radioactive: it forms from incoming cosmic radiation striking nitrogen (N¹⁴) in the atmosphere ( neutron + N¹⁴ = C¹⁴ + proton ). C¹⁴ is then absorbed by living tissue. No new C¹⁴ is absorbed once an organism dies. C¹⁴ constantly slowly breaks down through time: ( C¹⁴ = N¹⁴ + beta- particle). Thus the amount of C¹⁴ in dead animals and plants decreases over time and the older the animal or plant fossil the less C¹⁴ is present.

CRYSTAL FORM is the external expression of the orderly internal arrangement of atoms. If a mineral can grow unrestricted, it will develop individual crystals with well formed crystal faces.

Other important properties of minerals are: LUSTER, COLOR, STREAK, HARDNESS, CLEAVAGE, FRACTURE, SPECIFIC GRAVITY. Other properties include fluorescence, phosphorescence, solubility, magnetic, radioactivity, piezoelectric, and "magical power " according to some folks....

A comparison of quartz and calcite:

• Quartz is hard (covalent bonds) and forms in sedimentary, metamorphic, and igneous settings. It has a density of 2.7 g/cm3; it has an concoidal (glassy) fracture, and has a range of colors from clear to black (depending on impurities).
• Calcite is soft (in comparison to quartz). Calcite is a salt (ionic bonds). It breaks into rhombahedral crystal grains. It is precipitated from seawater by biogenic activity by a variety of plants and invertebrates. It also precipitates around hot springs.

ABUNDANCE OF ELEMENTS IN THE EARTH'S CRUST, p. 32

• Oxygen 46.6
• Silicon 27.7
• Aluminum 8.1
• Iron 5.0
• Calcium 3.6
• Sodium 2.8
• Potassium 2.6
• Magnesium 2.1
• All Others: 1.5

MINERAL GROUPS

SILICATES: (silicon-oxygen TETRAHEDRON, tetrahedrons form chains, double chains, and sheets.) See page 33

Common silicates are subdivided into groups:

• FELSIC silicates: "LIGHT" light colored, common in continental crusts, and have "low" density: Examples include: quartz, feldspar, and mica (muscovite).
• MAFIC silicates: "DARK" - dark colored, common in oceanic crust, "high" density; include olivine, pyroxene, and horneblend. The mafic silicate minerals are also referred to as ferromagnesian silicates.

BOWEN'S REACTION SERIES (p. 49, Chapter 3) - explains how the CRYSTALLIZATION process as magma cools, causes HIGH temperature minerals to form FIRST (mostly MAFIC minerals), and the LOW temperature minerals to form LAST (mostly FELSIC minerals). This causes the composition of the magma to change through time from mafic to more felsic. In a "magma chamber," a large volume of molten rock underground, this process is called MAGMATIC DIFFERENTIATION.

OXIDES

• Ice: H₂O
• Hematite: Fe₂O₃ (iron ore, "rust" - color in rocks)
• Magnetite: Fe₃O₄ (iron ore)

  SULFIDES

• Pyrite: FeS "fool's gold" - major source of sulfur (pollution, acids)
• Galena: PbS (lead ore)

  SULFATES (salts)

• gypsum: CaSO₄-2H₂0 (plaster) and anhyrite

  HALIDES (salts)

• Halite: NaCl (salt)

  CARBONATES

• Calcite: CaCO₃ ("reefs," limestone, marble, cement), Dolomite MgCa2(CO₃), and Malachite CuCO₃

  HYDROXIDES

• Bauxite: Al(OH)₃ (aluminum ore, soil)

  PHOSPHATES

• Apatite: Ca₅(F,Cl,OH)PO₄ (bone, explosives, fertilizer)

  NATIVE (PURE) ELEMENTS (Composed of a single element) - gold, silver, carbon (diamond, graphite, coal), copper, platinum, and sulfur

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