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I. Minerals
Essentials of Geology
Building blocks of rocks
A. Definition of a mineral
Minerals:
Building Blocks of Rocks
Chapter 2
1) Naturally occurring
2) Inorganic solid
3) Ordered internal molecular structure
4) Definite chemical composition
B. Definition of a rock
▪ A solid aggregate or mass of minerals
II. Composition of minerals (chemistry)
A. Basic Building Blocks of Chemsitry
1. Elements
▪ Basic building blocks of minerals
▪ Over 100 are known (92 naturally occurring)
2. Atoms
▪ Smallest particles of matter that retain all the
characteristics of an element
II. Composition of minerals (chemistry)
B. Structure of the Atom
1. Nucleus – center of the atom
▪ Consists of protons (positive charges) and neutrons
(neutral charges)
2. Electrons – rings around the atom
▪ Negatively charged particles that surround the
nucleus
▪ Located in discrete energy levels (basically rings)
called electron shells.
Halite (NaCl)
An example of ionic bonding
C. Chemical bonding
▪ Formation of a compound by combining two or
more elements. Like – H2O, CO2, SiO2. Sometimes
this can be two atoms of the same element, like
O2, Cl2.
1. Ionic bonding
▪ Atoms gain or lose outermost (valence) electrons
to form positively or negatively charged atoms
called ions.
▪ Oppositely charged ions attract to make ionic
compounds such as NaCl, sodium chloride (table
salt).
NaCl ionic bonds make
planes of weakness
where cleavage planes
appear.
In other words,
cleavage planes form
along planes of
weakness formed along
the ionic bonds.
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II. Composition of minerals (chemistry)
2. Covalent bonding
▪ Atoms share electrons to fill their outer
electron shell (ex. 8 out of 8 electrons)
▪ Covalent compounds are generally stronger
than ionic bonds
▪ Both ionic and covalent bonds typically occur in
the same compound
III. Structure of minerals
II. Composition of minerals (chemistry)
D. Isotopes and radioactive decay (very important in later
chapters)
1. Atomic Number – number of protons (ex. carbon
has 6 protons)
2. Mass number - the sum of neutrons plus protons
in an atom (most carbon has 12 – 6 p and 6 n)
3. An isotope is an atom that exhibits variation in its
mass number. (ex. carbon-13 has 6p and 7n;
carebon-14 has 6 p and 8n; C-14 decays to N-14)
4. Some isotopes have unstable nuclei that emit
radiation in a process known as radioactive decay
Figure 2.2
A. Crystalline structure - Minerals consist of an
orderly array of atoms chemically bonded to
form a particular crystalline structure. (recall
mineral definition – “Ordered internal molecular structure”)
1. Most minerals will have both ionic and covalent
bonding. Some bonds are weak and some strong.
2. This causes different minerals to have different
physical properties (like cleavage angles) and to
be classified into unique categories.
IV. Classification of minerals
Elemental abundances
in continental crust
• Nearly 4000 minerals have been identified on Earth, but we
will discuss only about 10 to 15 in this class.
A. Rock-forming minerals
• Common minerals that make up most of the
rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the 8 elements that make
up over 98 percent of the continental crust
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Silica tetrahedron
IV. Classification of minerals
B. Silicate Minerals (vs. Non-silicates)
1. Most important mineral group
▪ Comprise most of the rock-forming minerals (92%)
▪ Very abundant due to large amounts of silicon and
oxygen in Earth’s crust
Click here!
2. Basic building block is the silicon-oxygen
tetrahedron molecule
▪ Four large oxygen ions surrounding a much smaller
silicon ion
▪ Called “Silica” – SiO2 or SiO4-4
Figure 2.20
IV. Classification of minerals
C. Silica Tetrahedra
1. Covalent bonds of silicon to ½ of each oxygen give
silica tetrahedra (SiO4) an overall negative charge
of negative 4.
2. Single silica tetrahedra often link together to form
various structures:
▪ Isolated tetrahedra
▪ Ring structures
▪ Single and double chain structures
▪ Sheet or layered structures
▪ Complex three-dimensional structures
Models of Crystalline Structure
IV. Classification of minerals
D. Silica Tetrahedra structures tend to:
1. Have different degrees of negative charge that
need to be ionically bonded to positively
charged ions like these:
▪
▪
▪
▪
▪
▪
Aluminum - Al3+
Potassium - K1+
Sodium - Na1+
Calcium - Ca2+
Iron - Fe3+ or Fe2+
Magnesium - Mg2+
Minerals in the Crust
 Examples of crystalline structures (Click Here
for Models)
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Halite
Galena
Muscovite
Calcite
Quartz
Augite and Hornblende
Kaolinite (clay)
92% Silicates
8% non-silicates
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IV. Classification of minerals
E. Two main groups of silicates
Light (more felsic) silicates
Dark (more mafic) silicates
1. Light (more felsic) silicates
a) Lighter color, less dense, Silica plus Al, K, Ca, and Na.
b) Examples:
1.
2.
3.
4.
Feldspars – two main types - potassium feldspar [k-spar], and
plagioclase)
Quartz – pure silica
Muscovite (mica group) – sheets, silica, K, Al
Clay – complex chemistry, form from weathering
IV. Classification of minerals
F. Important nonsilicate minerals
1. Several major groups exist including
▪ Oxides
▪ Sulfides
▪ Sulfates
▪ Native elements
▪ Carbonates
▪ Halides
▪ Phosphates
IV. Classification of minerals
3. Important nonsilicate minerals
▪ Many nonsilicate minerals have economic value
▪ Examples
▪ Hematite (oxide mined for iron ore)
▪ Halite (halide mined for salt)
▪ Sphalerite (sulfide mined for zinc ore)
▪ Native Copper (native element mined for copper)
IV. Classification of minerals
E. Two main groups of silicates (continued)
2. Dark (more mafic) silicates
a) Called “Ferromagnesian” minerals – for iron (Fe) and
magnesium (Mg).
b) Darker color, more dense, silica plus Fe, and Mg.
c) Examples:
1.
2.
3.
4.
Olivine (peridote) – green, very high temperature of formation
Pyroxene – black, also very high temp (olivine and pyroxene
make up much of the mantle)
Amphibole – black, moderate temp
Biotite (black mica) – flaky mica, lower temp.
IV. Classification of minerals
2. Important nonsilicate minerals
▪ Carbonates
▪ Primary constituents in limestone and dolostone
▪ Calcite (calcium carbonate) and dolomite (calciummagnesium carbonate) are the two most important
carbonate minerals
Mineral resources
4. Mineral Resources – accumulation of abundant
minerals available for extraction.
• Resources includes:
– Reserves – already identified deposits
– Known deposits that are not yet economically or
technologically recoverable
• Common Mineral Resources:
– Gypsum, aluminum, copper, iron, gold, silver,
tungsten, lead, zinc, (not technically minerals –
coal and petroleum)
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Mineral resources
5. Ore - a rock containing a mineral that contains
valuable elements.
– Mineral and element must be highly
concentrated
– Profitability may change as economy changes
Mineral resources
• Almaden Quicksilver Mine location – San Jose/Morgan Hill
• Mineral Cinnabar: HgS (Mercury Sulfide)
• More money made from mercury than gold.
Mineral resources
• Click Here for QUEST video of AlmadenQuicksilver Mine
• http://www.kqed.org/quest/television/merc
ury-in-san-francisco-bay
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Oat Hill Mine Geology: The Howell Mountains are composed of Sonoma Volcanics
4,000 feet thick, with rhyolitic flows, including obsidian, near the top (USGS 2006).
The mercury ores in the Mayacmas mining district occur both in greywacke
sandstone of the Franciscan Complex at the Oat Hill and OHE mines, and in silicacarbonate altered serpentine at other nearby mines. The sandstone has been
hydrothermally altered primarily to kaolinite and quartz in the mineralized
area. Cinnabar is the primary ore mineral and usually occurs in association with
pyrite (FeS2) in this district. Calcite and quartz veins are present in the altered
sandstone and locally contain cinnabar. Elemental sulfur is present in the upper
part of the Oat Hill deposit which, along with kaolinite alteration, indicates that
the mercury ore formed in the steam-heated environment above the paleogroundwater table (USGS 2006).
Mercury ores at the OHE mine were mined from the eastern extension of veins
and mineralized fault zones of the Oat Hill mine. Thus, the ore grades were likely
similar at both mines, although specific information for ore grades at the OHE are
not available.
• Knoxville Mining District – McLaughlin Gold
Mine (Gold Mine)
• http://www.mindat.org/loc-218167.html
• http://nrs.ucdavis.edu/mcl/natural/geology/region/regi
on1.htm
• East Mayacmas District – Oat Hill Extension
Mine
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