Download Fig. 2-5, p.29

Monument Valley
Unit 1-CO, p.21
Quartz Crystals
Fig. 2-CO, p.22
 Vermiculite mine, Libby Montana.
 Discovered 1881, its properties make it valuable for packing,
insulation and as a soil additive (when heated it expands to
form a lightweight, fireproof, inexpensive material).
 Contaminated with asbestos: a mineral that is a known to cause
Fig. 2-1, p.23
cancer and lung disease.
 What is a mineral?
 naturally occurring, inorganic solid with a definite
chemical composition and a crystalline structure.
Fig. 2-2b, p.25
 naturally occurring: many
minerals can be manufactured
(e.g., synthetic diamonds).
 inorganic: do not contain
carbon-hydrogen bonds
(organic…plants and animals
create most of Earth’s organic
material)…what about coal and
oil? Shells of marine animals?
 solid: all minerals are solids.
Is water a mineral? Is ice a
mineral?
 chemical composition and
crystalline structure covered
next.
Granitic Rock, Bugaboo Mtns, BC
Canada
Fig. 2-2a, p.25
Elements, Atoms, and the Chemical
Composition of Minerals.
 Minerals are the building blocks of rocks, composed of
chemical elements.
 Element: fundamental component of matter, cannot be broken
down by ordinary processes. Most minerals are composed of
2-5 elements.
 Of the 88 naturally occurring elements in Earth’s crust, 8 make
up 98% of the crust: O, Si, Al, Fe, Ca, Mg, K and Na (see slide).
 Atom: basic unit of an element, and it consists of a nucleus (+)
surrounded by electrons (-). The nucleus of composed of
protons (+) and neutrons (no charge) (see slide).
 Ion: positively (cation) or negatively (anion) charged atoms.
Oxygen is commonly an anion and Earth’s abundant minerals
are commonly cations, so form compounds (of elements). Held
together by chemical bonds.
 So, minerals are compounds, usually 2-5 essential elements,
expressed as a chemical formula: SiO2 for quartz, contains one
silicon (+4) for every two oxygen (-2) atoms. Can you think of
an mineral that consists of only one element?
 The 88 elements
that occur naturally
in the Earth’s crust
can combine many
different ways to
form the more than
3,500 minerals
known. However,
the 8 abundant
minerals generally
combine in only a
few ways, resulting
in 9 rock-forming
minerals (or mineral
groups) that make
up most of the
Earth’s crust.
Table 2-1, p.28
 Electrons
concentrate in
layers or shells
around the
nucleus of an
atom.
Fig. 2-3, p.28
 When sodium (Na) and chlorine (Cl) atoms combine,
sodium loses one electron, becoming a cation (Na+);
chlorine gains the electron to become an anion (Cl-).
p.26
p.27
 Every mineral is a crystal (has a crystalline structure). It means
the atoms are arranged in a regular, periodically repeated
pattern.
 The mineral halite (common table salt; NaCl) has one Na for
every Cl atom. They alternate in orderly rows and columns that
intersect at right angles. This is its crystalline structure.
 Unit Cell: a small group of atoms, like a brick in a wall, repeats
itself over and over. Repeating bricks produce a rectangular
shaped wall (or some modification of a rectangle), similar to the
unit cell in crystals. Halite’s unit cell shown above.
Fig. 2-4, p.29
 Orderly
arrangement of
sodium and
chlorine ions in
halite (shows the
unit cell).
Exploded view.
Fig. 2-4a, p.29
 Show ions in
contact (halite
crystal).
Fig. 2-4b, p.29
 Shape of wellformed crystal
determined by
the shape of the
unit cell and the
manner in which
the crystal
grows. Stacking
of small cubic
unit cells could
produce the
cube (top) or
octahedron (8sided crystal) to
right. Not all unit
cells are cubic.
Fig. 2-5, p.29
 Halite crystals
showing crystalline
structure from
regular repeated
pattern of unit cells.
These crystals
probably grew
during evaporation
of salty seawater.
 This halite (to right)
shows welldeveloped crystal
faces (flat surface
that develops if a
crystal grows freely
in an uncrowded
environment).
Fig. 2-4c, p.29
 In nature the
growth of crystals is
often impeded by
adjacent mineral
grains. Minerals
rarely show perfect
development of
crystal faces. This
is a thin section of
granite, showing
that crystals fit
together like a
jigsaw puzzle.
Crystals grew
around others as
molten magma
solidified.
Fig. 2-6, p.29
Physical Properties of Minerals
 How do geologists identify minerals in the field?
Chemical and crystal structure analysis’ aren’t
practical in the field, so geologists rely on
physical properties to identify minerals, and can
use simple tests to confirm identification.
 These physical properties include crystal habit,
cleavage and fracture, hardness, color, luster,
specific gravity, streak and a few other
properties such as magnetism and reaction to
acid.
Crystal Habit
 Characteristic shape of a mineral, and the manner in
which aggregates of crystals grow. If it grows freely,
shape is controlled by arrangement of atoms (like
halite cubes). Above are equant crystals of garnet,
Fig. 2-7a, p.30
with same dimensions in all directions.
 Fibrous appearance of asbestos.
Fig. 2-7b, p.30
 Bladed crystals of kyanite.
Fig. 2-7c, p.30
 Some minerals occur in more than one habit. Quartz
grows as elongated crystals (left) and as massive
crystals with no characteristic shape.
Fig. 2-8, p.30
Cleavage
 Tendency of some minerals to break along flat surfaces. These
surfaces are planes of weak bonds in the crystal. Mica (for
example; above) has one set of parallel cleavage planes.
Minerals can have 1, 2, 3 or even four different sets of cleavage
Fig. 2-9, p.31
planes that can be described as excellent to poor and none.
 A flat surface created by cleavage, and a flat
surface that is a crystal face can appear
identical. Cleavage surface is duplicated
when a crystal is broken, a crystal face is not.
 Above: feldspar has two cleavages at right
angles; calcite has three sets of cleavage, not
a right angles (deformed box look); fluorite
has four cleavage planes (double pyramid
look); quartz has no cleavage (right), but
fractures.
Fig. 2-10, p.31
 Feldspar
Fig. 2-10a, p.31
 Calcite
Fig. 2-10b, p.31
 Fluorite
Fig. 2-10c, p.31
 Fracture: the manner in which a mineral breaks, not
along cleavage planes. Conchoidal fracture, shown
above (smoky quartz) creates smooth, curved
surfaces.
Fig. 2-11, p.32
 Hardness: resistance of a mineral to scratching
Table 2-11, p.32
Specific Gravity
 Weight of a substance relative to an equal
volume of water. Most common minerals have
a specific gravity of 2.7 (the mineral weighs 2.7
times that of an equal volume of water).
 Gold’s specific gravity is 19.
 Use “heft” to determine a mineral’s approximate
specific gravity.
Color
 Color is the most obvious property of a mineral,
but can be the most unreliable for identification.
Chemical impurities and imperfections in the
crystal structure can dramatically alter the color.
 Quartz, for example, can occur in many colors
including white, clear, black, purple and red as
a result of tiny amounts of impurities and minor
defects in the ordering of atoms.
Streak
 Streak is the color of the fine powder of a
mineral. Rub the mineral across a porcelain
plate called a streak plate. Many minerals
leave a diagnostic color.
 Hematite (iron oxide), for example, can be dull
red to shiny black in color, but it always leaves
a red powder on a streak plate (so can be more
reliable than color for identification).
 Luster:
This is the manner
in which a mineral
reflects light. A
mineral with a
metallic look has a
metallic luster.
Pyrite (to right)
has a metallic
luster. Nonmetallic luster can
be described by
terms such as
glassy, pearly,
earthy, resinous
and vitreous.
Fig. 2-12, p.13
Other Properties
 These include reaction to acid (calcite and
other carbonates liberate Co2), magnetism
(magnetite), radioactivity (uranium),
fluorescence (when exposed to utraviolet
light), phosphorescence and double refraction.
Mineral Classes and the Rock-Forming
Minerals
 Minerals are classified by their abundant
chemical elements (Table 2.3). Of all the
minerals, nine are the most common rockforming minerals in the crust. Seven are
silicates (containing silicon and oxygen) and the
other two are carbonates (containing carbon
and oxygen).
 Silicates: make up 92%
of the Earth’s crust.
Most abundant because
oxygen and silicon are
the most abundant
elements in the Earth’s
crust (and they readily
combine). Feldspars are
the most common
silicates, then pyroxene
and quartz. Silicate
tetrahedron commonly
link together by sharing
oxygen atoms.
Fig. 2-13, p.13
 Every silicon atom
in the Earth’s
crust surrounds
itself with four
oxygen atoms.
The bonds are
strong. This
pyramid shaped
structure is called
the silicate
tetrahedron, and
is the
fundamental
building block of
all silicate
minerals.
Fig. 2-13a, p.13
 Most silicate tetrahedra combine with additional elements
(cations such as aluminum, iron, calcium, potassium, sodium
and magnesium). Quartz is the only common silicate that
contains only Si and O. Silicate tetrahedra commonly link by
sharing oxygen atoms to form chains, sheets, or other threedimensional networks (Figure 2.14).
Fig. 2-13b, p.13
Table 2-3, p.34
 Rockforming
silicates fall
into five
main
groups,
based on
the way the
tetrahedra
link
together.
Fig. 2-14, p.15
 Feldspar alone makes up about half of the Earth’s
crust. Quartz composes 12% of the Earth’s crust, and
is widespread and abundant in continental rocks.
Fig. 2-16, p.36
 Olivine
Fig. 2-15a, p.36
 Pyroxene
Fig. 2-15b, p.36
 Amphibole
Fig. 2-15c, p.36
 Biotite
Fig. 2-15d, p.36
 Clay
Fig. 2-15e, p.36
 Feldspar
Fig. 2-15f, p.36
 Quartz
Fig. 2-15g, p.36
 Calcite: CaCO3
 A carbonate
mineral much
less common
than silicates in
the Earth’s crust,
but important
rock-forming
minerals
because found
in sedimentary
rocks across the
continents.
Fig. 2-15h, p.36
 Dolomite:
CaMg (C03)2
 Another
carbonate.
 Shells and
other hard
parts of many
marine
organisms are
made of
carbonate
minerals, and
accumulate to
form limestone.
Fig. 2-15i, p.36
Commercially Important Minerals
 Many minerals, although not abundant, are
commercially important. Our society depends on
metals such as iron, copper, lead, zinc, gold and silver.
 Ore minerals: minerals from which metals or other
elements can be profitably recovered. Gold and silver
occur as single elements; iron is bonded to oxygen;
copper, lead and zinc commonly bonded to sulfur.
 Industrial Minerals: commercially important, but not
considered an ore (not mined for metals). Examples
are halite mined for table salt; gypsum for ?; limestone
for ?; sulfur for?
 Gems: minerals of beauty (diamonds also used
industrially).
Galena is the most important ore of lead
Fig. 2-17, p.37
 Native sulfur occurs at vents of dormant and active
volcanoes.
Fig. 2-18, p.37
 Sapphire is one of the most costly precious gems
Fig. 2-19, p.38
 Topaz is a popular semiprecious gem
Fig. 2-20, p.38
Environmentally Hazardous Rocks and
Minerals
 Usually in their natural states, most rocks and
minerals are environmentally benign and
harmless to humans (or we wouldn’t survive). A
few are harmful and dangerous (asbestos for
example is cancer-causing).
 Most hazardous rocks and minerals are buried
and through natural processes are exposed so
slowly that they release toxic materials in low
concentrations. Irresponsible mining can
concentrate and release hazardous materials.
 One form of asbestos occurs as long, curly fibers.
Fig. 2-21a, p.39
 One form of asbestos occurs as short, sharply pointed
needles.
Fig. 2-21b, p.39
 Acid mine drainage can poison aquatic life and stain
stream beds and banks.
Fig. 2-22, p.41
p.42