GeoClassroom Physical Geology Historical Geology Structure Lab Mineralogy Petrology


Mineralogy Review

Minerals are those things which make up rocks. It is defined as:

1) a naturally occuring inorganic solid
2) it has a specific internal structure: the atoms are precisely arranged.
3) it has definite physical properties like hardness, form, etc. as a result of its crystalling structure and composition.
4) has a chemical composition which can be represented by a chemical formula.

-examples of minerals are quartz, diamond, ruby, gold, fools-gold, asbestos, etc.

ATOMS: consist of a nucleus with protons and neutrons. Proton has a + charge, while the neutron is electrically neutral. The surrounding cloud of electrons are negative.

    - For example, hydrpgen has one proton and one orbiting electron
    - Helium has 2 protons, 2 neutrons, and 2 orbiting electrons (e-)

ISOTOPES: Oxygen's atomic number is 8, and atomic weight is 16. Has 8 protons and 8 neutrons = 16. Isotopes of O have the same number of protons but different numbers of neutrons. DIFFER from O16 only in the number of neutrons.

    -some isotopes are naturally occuring but unstable, and as they decay, they emit radiation: these particles are those which participate in radioactive dating.

IONS: The gaining or loosing of electrons makes an atom an ion. It becomes positively charged if it looses and e-, and negatively charged if it gains and e-.

BONDING: 3 types of chemical bonding: ionic, covalent, and metallic. Atoms bond w/each other to form chemical COMPOUNDS like SiO2, Fe2O3, etc.

    Ionic bonding: One or more e- are transferred from one atom to another. One atoms gives up its e- to become stable, and the other atoms gains the e- to make itself stable. Ionic compunds consist of an orderly arrangement of oppositely charged ions as assembled in a definite ratio that provides overall electrical neutrality. NaCl is an example. Na needs to lose an e- to become stable, while Cl needs to gain an e- to become stable, so they combine to form NaCl.
    Covalent bonding: When atoms share e- to form a compound. SiO2 is an example of this. For example, two e- are shared in Cl2, in effect causing each Cl atom to gain 1 e- to become stable.
    Metallic bonding: In a metal, like Fe or Ag, e- are shared, but move freely around other ions, not atached to a specific ion. This gives metals special characterisitcs not found in other atoms. like electrical conductivity and the ability to be reshaped.

-There are nearly 4000 minerals out there, although no more than a dozen or so are abundant. These are termed the rock-forming minerals. Only 8 elements compose the bulk of these minerals and represent over 98% (by weight) of the continental crust.

-With minerals, the atoms are arranged in a specific 3D pattern, based on its chemical structure, called a crystal.

-While the size and shape of xls may vary, similar pairs of xl faces with in a particular xl (such as qz) always meet at the same angle. This is called the law of constancy of interfacial angles.

-Some substances can xllize into more than one type of structure, and this is called polymorphism. Carbon is an example, because it can xlize into graphite or diamond.

-And in a process called ionic substitution, 2 or more kinds of ions can substitute for each other in a mineral structure. For example, in the mineral olivine (Mg,Fe)2SiO4, ions of Fe and Mg can substitute freely for each other. The total number of Fe ad Mg is constant in relation to Si and O, but the ratio of Fe/Mg may vary from sample to sample.

-Xls tend to grow in a process called crystallization. They grow from solutions called melts to fill spaces in a rock. This process is similar to how ice grows on a pond. Each ice crystal competes for space on the pond, and the result is that some of the xls are nicely formed (cuz they had lots of space to grow into) and others are not nicely formed (no space available).

-Most minerals on this planet are Si-O based, unlike humans who are C based. In the earth, these elements are the most abundant:

O 46.6%
Si 27.7%
Al 8.13%
Fe 5%
Ca 3.6%
Na 2.8%
K 2.6%
Mg 2.1%
Ti 0.44%
H 0.14%
P 0.12%
Mn 0.10%
S 0.05%
C 0.03%

-Over 95% over the earth's crust is made up of silicate minerals (Si & O). These are linked to form a tetrahedron: 4 O to 1 Si

-These combine to form several fundamental configurations of tetrahedral groups. These are the four major silicate mineral groups:

    - Single chains
    - Double chains
    - 2D sheets
    - 3D frameworks

- In most of these groups, Fe, Mg, Na, Ca, K, Al combine with the Si and O in varying ratio to form different mineral. Each mineral has its own chemical formula and set of physical properties.

    - These physical properties are: xl form, cleavage, hardness, specific gravity, color, luster, and streak. We'll discuss these in lab.

- Other important minerals are:

    - Calcite CaCO3: Important mineral in fossils and shells of sea creatures
    - Clay minerals: Make up the finest sediment in rivers and streams
    - Halite NaCl: Table salt
    - Native Elements: Au, Cu, Ag, Pt, C (diamond and graphite)
    - Gemstones:
      diamond C
      emerald from a mineral called Beryl
      Ruby & Sapphire from Corundum
      Amethyst from quartz (SiO2)
    - Sulfides:
      galena PbS - lead
      sphalerite ZnS - zinc
      pyrite FeS2 - fools gold
      penlandite for Ni
      chalcopyrite CuFeS2 - copper

- Atoms combine to form compounds, and compounds combine to form minerals, and minerals combine to form ROCKS.

    - depending on the T,P, and composition of the melt, a rock may consist of several different minerals. Rocks are named based on their mineral compositions.
      GRANITE: quartz, orthoclase, plagioclase, muscovite, biotite, hornblende, plus a host of minor accessory minerals.
      BASALT: olivine, plagioclase, pyroxene
      LIMESTONE: calcite, dolomite (MgCaCO3)
      SANDSTONE: quartz, feldspar
      SLATE: clay minerals

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