Transcript Minerals

Minerals
Chapter 5
What is a mineral?
 Minerals are the building blocks of
rocks.. All of them are solid.
 They occur naturally and have a definite
chemical composition
 The atoms are arranged in an orderly
fashion (crystal)
 Inorganic (never alive)
How many minerals are there?
 Well, there about 4000 known but there
are a whole lot more I am sure to be
found.
 Minerals can be elements like lead or
compounds like feldspar
 Most are compounds
Elements of earth—native
elements
 Even though there are 92 elements that are
naturally found, only 8 elements make up more
than 98% of the earth’s crust.
 46.6% Oxygen (O)
27.7% Silica (Si)
8.1% Aluminum (Al)
5.0% Iron (Fe)
3.6% Calcium (Ca)
2.8% Sodium (Na)
2.6% Potassium (K)
2.1% Magnesium (Mg)
Compounds of the earth
 Most minerals are compounds.
 Quartz is the most common chemical
compound in the earth's crust. We know
it better as common beach sand. Si02
Mineral formation
 Process of crystallization
 Growth of a solid from a gas or liquid
whose constituent atoms come together
in the proper chemical proportions and
crystalline arrangement
When do minerals form?
 Cooling of magma (quartz)
 Precipitation from saturated solution
(halite)
 Atoms and ions become mobile an
rearrange themselves at high
temperatures
(pyroxene)
The earth, the other inner planets and the
moon are made of ROCKS.
Rocks in turn, are made of MINERALS
How are minerals formed?
 Minerals of one type of atom - native
elements (Au - gold, Ag - silver, Cu copper, among others).
 Minerals with cations combined with the
large, negative ions (anions): oxygen (O
- oxides), sulfur (S - sulfides), halogens
(Cl, F or Br - halides) .
 and anions groups made of oxygen
combined with cations of valency +3 or
greater (see periodic table - non-metals
of groups 13-17): silicates (SiO4),
carbonates (CO3) and sulfates (SO4).
Only a dozen minerals account
for most of the world's rocks.
 Plagioclase feldsparNaAlSi3O8 to
CaAl2Si2O8
 Potassium feldsparKAlSi3O8
 QuartzSiO2
 Pyroxene(Mg,Fe)2Si2O6 and
Ca(Mg,Fe)Si2O6 (augite)
 BiotiteK(Fe,Mg)3AlSi3O10(OH)2
 Hornblende(Ca,Na)2–
3(Mg,Fe,Al)5[(Si,Al)8O22](OH)2
 Olivine(Fe,Mg)2SiO4
 MagnetiteFe3O4
 Garnet(Ca,Mg,Fe2+)3(Al,Fe3+)2Si3O12
 CalciteCaCO3DolomiteCaMg(CO3)2
Physical properties of minerals
 Classifying minerals can range from
simple to very difficult. A mineral can be
identified by several physical properties.
 Sometimes minerals can only be
classified by chemical or X-ray diffraction
analysis; these methods, however, can
be costly, time-consuming, and even risk
damaging the sample.
Crystal structure
 See page 99
 It is the arrangement of atoms that
determines the shape…(just to repeat)
 Each mineral has its own unique form
 The angle at which crystal faces meet is
unique and can be used to identify the
mineral
Crystal structure
 Not all minerals form crystal faces….if
the space is limited when forming there
is no room for a “face” to form.
Silicates
 Minerals that contain oxygen and silicon
 May include other metallic elements
Staurolite, Fe2Al9O
 A few silicates do not have metal
included----quartz
 90% of all minerals are silicates
Silica tetrahedron
 The basic building blocks of all silicates
is the silica tetrahedron
Physical identification
 Crystal structure and habit: A mineral
may show good crystal habit or form, or
it may be massive, granular or compact
with only microscopically visible crystals.
Hardness:
 Mohs scale is relative and goes from 1 to
10. Minerals with a given Mohs hardness
can scratch the surface of any mineral
that has a lower hardness than itself.
The minerals that define the scale are
given below:
 1- talc 2- gypsum 3- calcite 4- fluorite 5apatite 6- orthoclase feldspar 7- quartz
8- topaz or beryl 9- corundum 10diamond
Mineral Properties
 luster hardness streak cleavage
fusibility specific
gravity habit tenacity color
luminescence radioactivity
magnetism
Luster
 A mineral’s luster is the overall sheen of
its surface – it may have the sheen of
polished metal, or that of an unpolished
metal that is pitted by weathering – or it
may have the sheen of glass, or look dull
or earthy, etc
Luster cont’d
 Adamantine, having the hard, sparkly look of a diamond
 Glassy/Vitreous, having the look of glass;
 Resinous, having the look of amber – not quite glassy;
 Pearly, having the iridescent look of mother-of-pearl
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(though usually just barely);
Greasy/Oily, having the look of an oil-coated substance;
Silky, having the look of silk, fine parallel fibers of mineral
– such as chrysotile "asbestos;"
Dull, having a plain looking surface that is not
submetallic;
Earthy, having the look of soil or clay
color
 a double-edged sword in mineral
identification: There are many minerals
which have distinctive colors; but there
are also many which come in a variety of
hues. And the same color can be seen
in several different species
Color cont’d
 Opalescence, an opal-like play of light,
reflections off the mineral
producing flashes of color that may
appear somewhat like a patch-work of
different "grains" of color that aren’t
really there: Move the sample minutely
and the color disappears from that spot.
Color cont’d
 Iridescence is similar to opalescence
except that it is usually associated with
metallic minerals and surface reflections
rather than glassy minerals and subsurface reflections: An exception is the
type of iridescence known as
labradoresence
Color cont’d
 Luminescence is the emission of light
by a mineral other than the reflected light
of the sun or a lamp – the mineral
"glows" due to some other reason.
Chatoyancy
 Chatoyancy is the play of light off
closely packed parallel fibers or parallel
inclusions in cavities. The light reflects
along lines – which may be straight or
curved – giving the mineral a somewhat
silky appearance. This characteristic is
seen in such minerals as "satin spar"
gypsum, "tiger’s eye" (fibrous crocidolite
replaced by quartz), and chrysoberyl
Fusibility
 The measure of how much heat it takes
to melt a mineral into a globule, or at
least to melt the sharp edge of a sharp
splinter and make it round over.
specific gravity
Density and Specific Gravity are not properties
easily determined, requiring special equipment.
"heft" can come in handy: The denser a mineral
is, the heavier it is per given volume. A 1 inch
cube of galena is noticeable heavier in the hand
than a 1 inch cube of pyrite. With a little
practice a collector can become good judging
the relative weight of minerals and using that to
help establish a sample’s identity.
habit
 Habit is the general appearance a
mineral tends to have – whether it is
found as blocky crystals, long slender
ones, or aggregates of some type, etc.
 Distinct crystals may be described by the
following……..see website
Tenacity
 refers to a mineral’s resistance to
breaking, bending, or otherwise being
deformed. A mineral may be:
 brittle, malleable, sectile, flexible,
elastic,
Streak
 Streak is simply the color of a mineral
powder. Many minerals have a different
color when powdered than they do in
crystal or massive forms. The color may
be entirely different, or it may be a
different shade.
specific gravity
Density and Specific Gravity are not properties
easily determined, requiring special equipment.
"heft" can come in handy: The denser a mineral
is, the heavier it is per given volume. A 1 inch
cube of galena is noticeable heavier in the hand
than a 1 inch cube of pyrite. With a little
practice a collector can become good judging
the relative weight of minerals and using that to
help establish a sample’s identity.
Cleavage
 Cleavage refers to the way some
minerals break along certain lines of
weakness in their structure.
Radioactivity
 is another property that, while not too
common, is found in some minerals and
can be useful in identification. Collectors
who have a Geiger counter may find it
useful at certain localities, particularly
pegmatite – where many of the more
common radioactive minerals are found.
Fracture
 Minerals break in directions other than
along cleavage surfaces
 Conchoidal—shell like--smooth
 Splintery—leave jagged edge
 Uneven or irregular—rough surface
Chemical tests
 Reaction with acid—calcite (CaCO3)
fizzes and releases carbon dioxide gas
Special properties
 Double refraction—causes a single
object to appear as two
Simple kit
 A piece of plain white paper (a blank specimen label
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works great.)
Your fingernails (preferable still attached to your fingers!)
A copper penny (or small –½ inch – piece of copper or
short piece of heavy copper wire.)
A small piece of fluorite (a broken cleavage piece is fine.)
A pocket knife (NOT a Swiss Army knife – the steel in
those is harder than in most cheap pocket knives, which
can throw hardness tests off.)
A small section of a steel file (a 2 or 3 inch tip from a
triangular file for sharpening chain saws works fine.)
A piece of a quartz crystal (with at least one good face
and a sharp point - a broken section
Simple kit cont’d
 usually has a sharp point on it somewhere, it doesn’t have to be
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a crystal termination.)
A small piece of a beryl or topaz crystal (with at least one good
face and a sharp point or edge.)
A small piece of a corundum crystal (with at least one good face
and sharp point or edge.)
A "streak plate" (unglazed porcelain tile – a 2 inch square is
plenty.)
A short candle stub and matches (in waterproof container) or a
cigarette lighter.
A small pair of tweezers.
A small magnet (a refrigerator magnet is fine, but should be a
fairly strong one.)
A 10x hand lens/jeweler’s loupe.
Blank specimen labels.
Pens or pencils.
Mineral groups
 Major silicates comprise 90% of earth
minerals
 Classified by ways the tetrahedral linked
together see page 101
Quartz
 Entirely tightly bound silica tetrahedral
 Glass or greasy luster
 Pure quartz-colorless or white
 Colored quartz—amethyst, rose, smoky,