Minerals
mineral = naturally occurring inorganic solid with
characteristic chemical composition & crystalline
structure
Five Characteristic of Minerals
1. occurs naturally
2. inorganic (not made up of living things or remains
of living things)
3. solid
*4. characteristic chemical composition
*5. crystalline pattern = atoms arranged in a pattern
repeated over and over
* these properties are most important because they
distinguish any mineral from all others
KINDS OF MINERALS
1. more than 3000 different minerals identified so far
(only 30 are common)
2. rock-forming minerals = common minerals that form
the rocks of earth’s crust
3. 10 minerals make up 90% of earth’s crust: quartz,
orthoclase, plagioclase, muscovite, biotite, calcite,
dolomite, halite, gypsum, and ferromagnesian
minerals
4. classified into two main groups based on chemical
composition
Minerals from magma:
1. magma = molten material found beneath Earth’s
surface
2. type and amount of elements in magma determine
type of minerals formed
3. rate at which magma cools determines size of
mineral crystals
a. small crystals → cools rapidly
b. large crystals → cools slowly
Mineral from solution:
1. a given amount of water can only dissolve so much
of a solid
2. when water becomes supersaturated (too much)
with another substance, mineral crystals may begin
to precipitate out of solution
3. can also be formed when water evaporates away
leaving mineral behind to form crystals
halite
Mineral groups:
silicates = all minerals containing silicon and oxygen
[oxygen most abundant element in crust; silicon
second most abundant]
1. usually contains one or more other elements
2. most abundant - 96% of Earth’s crust
3. feldspar and quartz alone make up 50% of earth’s
crust
4. types:
a. feldspars - most common
1) orthoclase = K
2) plagioclase = Na or Ca or both
b. quartz = pure silicon and oxygen
c. ferromagnesian minerals - rich in Fe and Mg
1) include hornblende, olivine, muscovite, biotite
orthoclase
quartz
biotite
nonsilicates = minerals that do not contain silicon
1. carbonates = has carbonate groups (CO3) & other
elements
a. primary minerals found in rocks such as
limestone, coquina
b. some have distinctive
colorations
malachite
[azurite – blue]
Ex: calcite, malachite
Gypsum crystals
2. sulfates = has a sulfate group
(SO4) and other elements
Ex: gypsum
3. halides = other elements with either chlorine,
fluorine, iodine, and bromine
fluorite
Ex: halite, fluorite
4. oxides = metal element combined
with oxygen
Ex: hematite, magnetite
5. sulfides = metal element combined
with sulfur
pyrite
Ex: pyrite, chalcopyrite
6. native elements = uncombined
elements
Ex: copper, sulfur
copper
CRYSTALLINE STRUCTURE
crystal = natural solid with a definite shape
1. characterized by specific geometric arrangement of
atoms
2. position of atoms inside solid produce visible
shape
3. X-rays are used to study crystal structure
Quartz crystal
4. all silicate mineral structures have same building
block
a. basic unit is the silica tetrahedron
(silicon-oxygen tetrahedron)
1) silicon atom surrounded by 4 oxygen atoms
2) forms pyramid shape with silicon in middle and
oxygen at 4 corners
b. combines in different
arrangements to produce
different minerals
c. three types of tetrahedra arrangements
1) ionic = tetrahedrons linked only by atoms
other than Si and O
2) chains:
a) single-chain = tetrahedron bonded to two
others by shared oxygen atoms
- called pyroxenes
b) double-chain = 2 single chains bond to each
other
- called amphiboles
3) sheets = each tetrahedron shares three
oxygen atoms with other tetrahedra
d. network silicates = each tetrahedron is bonded to
four neighboring tetrahedra
mineralogy = study of minerals and their properties
mineralogists = scientists who specializes in the study
of minerals
MINERAL IDENTIFICATION
Identification by inspection:
1. color = first and most easily observed property
a. only reliable for those that are the same color
b. usually isn’t enough to identify a mineral
c. impurities can change mineral to various other
colors
Ex: corundum = colorless
corundum + Cr = ruby
corundum + Co + Ti = sapphire
d. weathered surface may hide color
e. need to inspect a freshly exposed surface
2. luster = describes how light is reflected from
mineral’s surface
a. metallic = reflect light like polished metal
Ex: pyrite, galena
b. nonmetallic = do not reflect much light
1) usually described by self explanatory words
2) include dull (earthy), pearly, silky, brilliant,
glassy (vitreous), transparent, waxy (resinous),
adamantine, greasy, and oily
3. texture = how mineral feels to the touch
a. used in combination with other tests
b. describe as: rough, smooth, ragged,
greasy, soapy, or glassy
4. crystal habit = characteristic shape and the manner
in which its crystals grow together
a. controlled by the arrangement of the atoms
b. some can have more than one habit
c. crystals need space to grow to develop its shape
1) when growth is obstructed the shape is
changed
2) perfectly formed crystals are rare
d. crystal faces = flat surface that forms if a crystal
grows without obstruction
e. six crystal systems: Table 4-1, p.78
1) defined by 3 or 4 imaginary axes
that intersect at the center of
perfect crystal
2) called crystallographic axes
Identification by simple tests:
1. hardness = measures how easily a mineral can be
scratched
a. controlled by strength of bonds in mineral
b. measured by attempting to scratch unknown
mineral with object of known hardness
1) if object scratched unknown → unknown is
softer than object
2) if object does not scratch unknown → mineral
is harder than object
c. Moh’s Scale of Hardness = lists hardnesses of ten
minerals
1) developed by Friedrich Mohs
2) softest mineral = 1, hardest = 10
3) can use these reference minerals to determine
an unknown
d. during field work use common objects to test
penny = 3.5
common nail = 4.5
fingernail = 2.5
window glass = 5.5
pocketknife = 5.0
steel file = 6.5
e. be sure to check for scratch since powder may rub
off from softer minerals
Mineral test kit
2. streak = color of a mineral’s powder
a. obtained by rubbing mineral across piece of
unglazed white porcelain tile = streak plate
b. streak will always be same color even though
color of mineral may change
c. streak color can be different from color of mineral
Ex: hematite can be brown, red, or silver → its
streak is always reddish-brown
d. as a rule
1) metallic minerals generally have a dark streak
2) nonmetallic minerals will have streak that is
usually colorless or very light shade of normal
color
e. test works only for minerals softer than tile
f. if mineral has hardness greater than 7, it will not
streak
3. way a mineral breaks
a. cleavage = tendency to split easily or
to separate along flat surfaces
Ex: mica, fluorite
b. fracture = break with rough or
jagged edges or surfaces
1) conchoidal = break into smooth,
curved surfaces
Ex: quartz, obsidian
2) splintery or fibrous = leaves
a jagged surface with
sharp edges
Ex: copper
3) irregular (uneven) = leaves a rough surface
Ex: cinnabar
4. density: helps identify heavier minerals more readily
than lighter ones
5. specific gravity = weight of a mineral relative to that
of an equal volume of water
a. nearly all minerals are denser than water
b. typical nonmetallic minerals are slightly
less than 3
c. typical metallic minerals are about 5 or greater
d. heft = determine density / specific gravity of a
mineral by picking up to judge mass
1) must practice with known minerals to develop the
feel
2) higher the specific gravity or denser minerals will
feel heavier
Formula:
specific gravity =
weight of sample in air
weight of equal volume of water
= weight of sample in air
loss of weight in water
Example:
A specimen weighs 50 newtons (N) in air and 30 N in
water. What is the specific gravity of the specimen?
weight in air = 50 N
weight loss = 50 N - 30 N = 20 N
sp. = 50 N = 2.5
20 N
The specimen is 2.5 times as heavy as an equal
volume of water.
Unique Properties:
1. magnetism = small particles of iron - containing
minerals react to magnet
Ex: magnetite - most common
lodestone - acts as a magnet
2. double refraction = splits light rays into 2 parts
a. one ray travels straight through and the other ray
is bent
b. causes two images to be seen when an object is
viewed through transparent specimen
Ex: calcite
c. refraction = bending of light rays as they pass
from one substance to another
3. acid test = specimen reacts producing bubbles
a. referred to as effervescence
b. use a weak hydrochloric acid solution
c. shows substance contains carbonate
Ex: calcite
4. fluorescence = ability to glow under ultraviolet light
Ex: fluorite
5. phosphorescent = continue to glow after the
ultraviolet light is turned off
Ex: sphalerite
6. radioactivity = gives off radiation due to unstable
nuclei decaying
a. can be detected with a Geiger counter
b. pitchblende - most common mineral with
uranium
c. others include carnotite, uraninite, autunite
7. taste = has a characteristic flavor
Ex: halite
8. smell = has a characteristic odor
Ex: sulfur
9. how sounds when tapped
Ex: jade
Mineral Uses:
ore = mineral that contains a useful substance that can
be mined for a profit
Ex: hematite = iron;
bauxite = aluminum
1. mines are used to remove
minerals underground
bauxite
2. classification of mineral as
an ore can change if supply or
demand for mineral changes
hematite
gemstones = minerals that are prized for their beauty
rather than for industrial use
1. have exceptional brilliance, color, durability, and
rarity
2. once cut and polished it is called a gem
3. used in jewelry
4. two types:
a. precious stones = rarest and most valuable
Ex: emeralds, diamonds, rubies, sapphires
b. semiprecious stones = more common, so are not
as rare and valuable
Ex: amethyst, garnet,
opal
turquoise, opal
5. in its natural form it may look quite different from a
gem
6. different from common form of same mineral:
a. elements from which it is made
Ex: manganese in quartz → purple amethyst
b. arrangement of elements → crystal structure
1) allows it to be cut and polished
2) provides information about the internal
structure
7. a few gems are not minerals
Ex: pearls, amber