Download Mineral Groups

Matter and Minerals
Minerals: Building blocks of
rocks
•
•
•
•
Naturally occurring
Solid
Inorganic
Definite chemical
composition
• Crystal structure due
to internal
arrangement of atoms
http://www.minerals.net/gemstone/index.htm
General Facts about Minerals
• Between 2 - 3,000 have been identified
• A few are “native elements” -- made of only
one element, such as sulfur, gold. copper,
and graphite (carbon)
• Most are compounds, especially the silicate
group (Si, O).
• Other important groups are oxides,
carbonates, and sulfides.
Less than a dozen are common in
most rocks
• Quartz
• Feldspar (group)
• Muscovite (white
mica)
• Biotite (black mica)
• Calcite
• Pyroxene
• Olivine
• Amphibole (group)
• Magnetite, limonite,
and other iron oxides
• Pyrite
How do we identify minerals?
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Physical properties:
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Color
Luster
Hardness
Crystal shape
Cleavage
Specific gravity
Other
Physical Properties of Minerals
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Color:
– Most obvious, but often misleading
– Different colors may result from impurities
Example:
Quartz
A mineral can be many different
colors. Below is Mica.
Many minerals can be the same color.
Below are gold colored minerals. Which
one is gold?
Physical Properties of Minerals
•
Color:
Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching
a mineral on a piece of
unglazed porcelain.
Example:
Hematite
Gold
• When gold is run
across a streak
plate it makes a
yellowish-gold
color.
Pyrite or “Fool’s Gold”
• When pyrite is run
across a streak
plate, it has a
black or dark green
streak.
• Pyrite is not worth
much money, while
gold is worth a lot.
They look alike, so
miners call it fool’s
gold.
Hematite
• Hematite’s color is
grey, but its streak
is red.
• Hema means
blood.
• The mineral was
named hematite
because it looked
like it was bleeding
when it was taken
across a streak
plate.
Physical Properties of Minerals
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Luster:
– How a mineral surface reflects light
– Two major types:
• Metallic luster
• Non-metallic luster
Metallic
example:
Galena
Non-metallic
example:
Orthoclase
Pyrite has metallic luster
Quartz has vitreous luster
Physical Properties of Minerals
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Hardness:
– How easy it is to scratch a mineral
– Mohs Scale of Hardness
• relative scale
• consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of Hardness
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5)
- Copper coin (3.5)
- Wire nail (4.5)
- Glass (5.5)
- Streak plate (6.5)
Gypsum is soft, it can be scratched by
a fingernail.
Calcite is soft, but a little harder
because it cannot be scratched by a
fingernail, but it can be scratched by a
coin
Fluorite is harder. It can be scratched
by a nail, but not a coin or fingernail.
Diamond is the hardest mineral, so
it scratches every mineral.
Physical Properties of Minerals
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Crystal shape (or form):
– external expression of a mineral’s internal
atomic structure
– planar surfaces are called crystal faces
– angles between crystal faces are constant for
any particular mineral
Quartz
Pyrite
Physical Properties of Minerals
•
Cleavage vs. Fracture:
– The way a mineral breaks
– Cleavage: tendency of a mineral to break
along planes of weakness
– Minerals that do not exhibit cleavage are said
to fracture
Do not confuse cleavage planes with crystal faces!
Crystal faces are just on the surface and may not
repeat when the mineral is broken.
Physical Properties of Minerals
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Cleavage is described by:
– Number of planes
– Angles between adjacent planes
– These are constant for a particular mineral
Physical Properties of Minerals
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Cleavage (1 direction):
Example: mica
Physical Properties of Minerals
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Cleavage (2 directions):
orthoclase
amphibole
Physical Properties of Minerals
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Cleavage (3 directions):
halite
calcite
Physical Properties of Minerals
•
Cleavage (4 directions):
fluorite
Physical Properties of Minerals
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Fracture:
– minerals that do not exhibit cleavage are said to
fracture
– smooth, curved
surfaces when
minerals break in a
glass-like manner:
conchoidal fracture
Quartz
Physical Properties of Minerals
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Specific gravity:
– weight of a mineral divided by weight of an
equal volume of water
– metallic minerals tend to have higher specific
gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67
Mineral properties
•
PHYSICAL CHARACTERISTICS:
Specific Gravity S.G. is an easily measured physical property that can be readily estimated. In general,
sulphides and oxides have much higher specific gravities than silicates.
MINERAL GROUP
Framework Silicate
Framework Silicate
Sheet Silicate
Chain Silicate
Chain Silicate
Isolated Silicate
Isolated Silicate
Sulphide
Sulphide
Sulphide
Oxide
Oxide
Sulphide
Oxide
Element
MINERAL
Quartz
Feldspar
Mica
Amphibole
Pyroxene
Olivine
Garnet
Sphalerite
Chalcopyrite
Pyrite
Magnetite
Hematite
Galena
Pitchblende
Native Gold
SPECIFIC GRAVITY
2.6-2.7
2.6-2.7
2.8-3.0
2.9-3.2
3.2-3.6
3.3-4.4
3.5-4.4
4.0
4.2
5.0
5.2
5.3
7.2
9.5
12.4
Physical Properties of Minerals
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Other properties:
– reaction with hydrochloric acid (calcite fizzes)
– taste (halite tastes salty)
– feel (talc feels soapy, graphite feels greasy)
– magnetism (magnetite attracts a magnet)
Mineral Groups
•
Rock-forming minerals
– ~30 common minerals make up most rocks in
Earth’s crust
– Composed mainly of the 8 elements that
make up over 98% of the crust
Mineral Groups
Element Abundances
SILICATES
Silica
(SiO4)4-
Common cations that
bond with silica anions
All others:
1.5%
Common Silicate mineral groups
mineral
Olivine
formula
(MgFe)2SiO4
cleavage
none
Pyroxene
(Mg, Fe) SiO3
Amphiboles:
Eg. hornblende
Mica
Muscovit
e
Biotite
(Ca2Mg5)Si8O22(OH)
two cleavage
planes at 900
Two planes at
600and 1200
One plane
2
KAl3Si3O10(OH)2
Silicate structure
Single
tetrahedron
chains
Double chains
sheets
K(MgFe)3Si3O10(OH)
2
Feldspars:K-feldspar
Orthoclase,
microcline
Plagioclase
Quartz
KAlSi3O8
Two planes at 900
Three dimensional
networks
none
Three dimensional
network
(Ca,Na)AlSi3O8
SiO2
Common Non Silicate mineral groups
group
Oxides
member
Magnetite
Haematite
Corundum
formula
Fe3O4
Fe2O3
Al2O3
uses
Ore of iron
Ore of iron
Abrasive
Sulphides
Galena
Sphalerite
Pyrite
PbS
ZnS
FeS2
Ore of lead
Ore of zinc
Fool’s gold
Sulfates
Gypsum
Anhydrite
CaSO4.H2O
CaSO4
Used for plaster
Native elements
Gold
Silver
Copper
Sulfur
Graphite
Au
Ag
Cu
S
C
Precious metal
Precious metal
Used for Wires
Used in chemicals
pencils
Halides
Halite
Flourite
NaCl
CaF2
Common salt
Used in chemicals
Carbonates
Calcite
CaCO3
Used in cement
Mineral Groups
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Silicates (most abundant)
Non-silicates (~8% of Earth’s crust):
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–
–
–
–
–
Oxides
Carbonates
Sulfides
Sulfates
Halides
Native elements
O2(CO3)2S2(SO4)2Cl-, F-, Br(single elements; e.g., Au)
Mineral Groups – Silicates
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Silicates
– Tetrahedron
• fundamental
building block
• 4 oxygen ions
surrounding a
much smaller
silicon ion
Silicon-oxygen
tetrahedron
(SiO4)4-
Mineral Groups – Silicates
•
Joining Silicate Structures
– How tetrahedra may be linked:
• independent tetrahedra
• single chains
• double chains
• sheets
• 3-D framework
Mineral Groups
– Silicates –
Mineral Groups – Silicates
Olivine Group
dark silicates (Fe-Mg)  ferromagnesian
No cleavage
Composition
Magnesium iron silicate. The series ranges from
the magnesium end member, Forsterite, through
the intermediate member, Olivine (also known as
Chrysolite), to the iron end member, Fayalite
The Olivine group is composed of three minerals, with the
following formulas:
Forsterite = Mg2SiO4
Olivine (Chrysolite) = (Mg,Fe)2SiO4
Fayalite = Fe2SiO4
The intermediate variety, Olivine, is not scientifically
recognized as a separate mineral, but is nevertheless
mentioned.
Color
Streak
Hardness
Crystal Forms
and Aggregates
Transparency
Specific Gravity
Luster
Cleavage
Fracture
Tenacity
Olive-green, yellow-green, light
green, yellow, yellow-brown,
brown, gray, white
Colorless
6½ - 7
Usually occurs as rounded
grains, in dense aggregates of
grainy crystals, and as fractured
masses.
Transparent to translucent
3.2 - 4.2
Vitreous
none
Conchoidal
Brittle
Uses
Striking Features
Complex Tests
The variety Peridote is a famous
gem. It creates a distinctive,
yellow-green to olive-green gem
that is well known. It is the
birthstone for August.
Olivine is also used as a flux for
making steel, and is an ore of
magnesium.
Color, localities, and hardness
Soluble in hydrochloric acid
Mineral Groups – Silicates
Pyroxene Group
Ferromagnesian / dark silicates (Fe-Mg)
Augite
2-directions
of cleavage
(at nearly 90 degrees)
Minerals
The typical pyroxene structure
contains chains of SiO3
tetrahedrons
•
The slope of the tetrahedral
pyramids helps to determine
the cleavage angle of the
pyroxenes at nearly 90o
degrees (actually 93o and
87o).
Pyroxene minerals are common in in meteorites and the
extrusive igneous rock called basalt. There are many
different types of pyroxene including augite, wollastonite,
diopside, enstatite, and hypersthene. All of the types contain
Si2O6 but some have sodium (Na) while others have iron
(Fe), magnesium (Mg), or a combination of these three
elements . The general properties of the more common
pyroxene minerals, such as augite, are listed below.
Shape:Orthrorhombic or Monoclinic
Luster: Glassy or metallic
Color: Black
Streak: White, light green or light brown
Hardness: 5-6.5 on Mohs hardness scale
Cleavage: Two planes that meet at nearly a 90-degree angle
Fracture: Most have uneven and brittle fractures.
Mineral Groups – Silicates
Amphibole Group
Ferromagnesian / dark silicates (Ca, Fe-Mg)
Hornblende
2-directions
of cleavage
(not at 90 degrees)
There are several different minerals within the amphibole
group, but the most common type is hornblende. You can
find small crystals of hornblende in many types of igneous
rocks. They often look like little dark specks.
Hornblende (Ca2Mg5)Si3O22(OH)2
Shape: Monoclinic (crystals look like short, six-sided
columns)
Luster: Glassy or milky
Color: Black or dark green, translucent to opaque
Streak: Grey-green or grey-brown
Hardness: 5-6
Cleavage: Two planes that meet at a 124-degree angle
Fracture: Uneven brittle fracture
Mineral Groups – Silicates
Mica Group and Clay Minerals
light silicates (K, Al)  non-ferromagnesian
Muscovite
1-direction
of cleavage
Minerals
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Micas and Clay Minerals
Sheets of tetrahedra are the
building blocks. Aluminum
is also involved in thesesheet
structures which are chargebalanced by the cations Mg,
Na and K.
most common mica
minerals:muscovite , biotite
Mica minerals make some rocks sparkle! They are often found in
igneous rocks such as granite and metamorphic rocks such as schist.
They sparkle because light is reflected on their flat surfaces, which are
where the mineral breaks along its plane of cleavage. These minerals
break so easily along their cleavage that some crystals have broken into
many thin layers that look like the pages of a little book.
Biotite
K(MgFe)3Si3O10(OH)2
•Shape: Monoclinic.
Forms flat plates.
•Luster: Pearly, metallic
•Color: Dark brown, dark
green or black
•Streak: White
•Hardness: 2.5-3
•Cleavage: Yes,
•one plane of cleavage
•Fracture: The mineral is
rather flexible and so it
doesn’t fracture very
easily. In fact you can
bend it very far before it
breaks.
Muscovite
KAl3Si3O10 (OH)2
•Shape: Monoclinic. Forms flat
plates.
•Luster: Pearly, metallic
•Color: Colorless or lightly
tinted
•Streak: White
•Hardness: 2-3 on Mohs
Hardness Scale
•Cleavage: Yes, one plane of
cleavage
•Fracture: This mineral is also
flexible and doesn’t fracture
very easily.
Mineral Groups – Silicates
Feldspar Group
K-feldspar
light silicates (K-Na-Ca, Al)
Most common mineral group
Orthoclase
Plagioclase
2-directions
of cleavage
(at 90 degrees)
Ca/Na-feldspar
Minerals
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Feldspar group
A second group of aluminosilicates, tetrahedra form
three-dimensional
frameworks with Ca, Na and
K as the balancing cations.
The very abundant
feldspar are K-Na bearing
alkali
The K-feldspars or alkali felspars:
•Microcline, (Potassium aluminum
silicate)
•Orthoclase, (Potassium aluminum
silicate)
Feldspar is the most common mineral in the Earth’s crust, so you
are very likely to find it in the rocks you collect! It is found it all
of the three rock types, but is most common in intrusive igneous
rocks like granite where the crystals look white or pink.
There are several types of feldspar. The characteristics of the two
most common types are listed below. These two common types of
feldspar are difficult to tell apart besides their color. Color can be
helpful, but beware because the same mineral can often have
different colors. The sure way to tell these two apart is by looking
at the crystal surfaces for thin parallel groves called striations.
Plagioclase feldspar has striations but orthoclase feldspar does
not.
Orthoclase K AlSi3O8
•Shape: Monoclinic (Flat tabular or prism-shaped crystals)
•Luster: Glassy or pearly
•Color: Cream to pink
•Streak: White
•Hardness: 6 on Mohs Hardness Scale
•Cleavage: perfect
•Fracture: brittle
Plagioclase CaNaAlSi3O8
•Shape: Triclinic (Single prism-shaped crystals are very rare. You are
much more likely to find many crystals that have grown together in a
mass.
•Luster: Glassy or pearly
•Color: White to gray
•Streak: White
•Hardness: 6-6.5
•Cleavage: perfect
•Fracture: brittle
Mineral Groups – Silicates
Quartz
light silicates (pure SiO2)
no cleavage
(conchoidal fracture)
hard, resistant to weathering
Quartz
Quartz is one of the most common mineral in Earth’s crust!
Silica (Si) and Oxygen (O) are the only elements within pure quartz.
Quartz can be found in all sorts of rocks. Most sand is made of quartz
because it is hard and does not weather away easily. Some pieces of
quartz are white like milk but most are clear like glass, sometimes with a
little pink or grey tinge of color.
Quartz
Shape: Trigonal (Perfect crystals are usually 6-sided prisms with a
pyramid shape at the end. However, it is much more common to find
many crystals that have grown in a mass or broken crystals.)
Luster: vitreous
Color: Colorless or white. Some varieties are pink or smoky.
Streak: White
Hardness: 7
Cleavage: None
Fracture: Conchoidal
Minerals
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•
Quartz
Silica tetrahedra alone can
form a neutral threedimensional framework
structure with no need for
other cations.
This arrangement forms a very
stable structure
popular as ornamental stone and as gemstones
•Amethyst is the purple gemstone variety.
•Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating
Amethyst.
•Milky Quartz is the cloudy white variety.
•Rock crystal is the clear variety that is also used as a gemstone.
•Rosey Quartz is a pink to reddish pink variety.
•Smoky quartz is the brown to gray variety.
Mineral Groups
Non-ferromagnesian
Silicates (K, Na, Ca, Al)
Ferromagnesian
Silicates (Fe, Mg)
Oxides
Carbonates
Sulfides/sulfates
Native elements
Minerals
There are a few important groups of non-silicate minerals.
Only the carbonates are significant as rock-forming minerals. The
remaining mineral groups are often ore minerals and provide
economic sources for various elements.
The important non-silicate groups are:
–
–
–
–
–
Carbonates
Evaporites
Oxides
Sulphides
Phosphates
Minerals
Non silicates:
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•
•
•
Carbonates Co3
The important carbonates are the minerals calcite and dolomite. Both are significant
rock-forming minerals.
The calcite group
Calcite (Calcium Carbonate)
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•
•
•
Magnesite(Magnesium Carbonate)
Rhodochrosite (Manganese Carbonate)
Siderite(Iron Carbonate)
Smithsonite (Zinc Carbonate)
Minerals
Non silicates:
• Evaporites:
including the minerals halite, and fluorite;
Sulphates including the minerals gypsum and anhydrite.
The most famous halide mineral, halite (NaCl) or rock salt
Minerals
Non silicates:
• Evaporites
•Fluorite: CaF2, Calcium Fluoride
Minerals
Non silicates:
•Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate
Minerals
Non silicates:
•
•
Oxides
oxides (hematite and magnetite)
Fe2O3, Iron Oxide
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•
•
•
hydroxides (limonite and goethite)
important minor constituents in rocks.
aluminum oxide bauxite can also occur as a rock-forming mineral.
oxide minerals are exploited as economic sources of many elements including aluminum,
antimony, iron, manganese, tin, and uranium.
Minerals
Non silicates:
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•
•
•
Sulphides
The mineral pyrite is the only sulphide that occurs commonly in rocks.
Sulphides are most important as economic minerals providing the main sources of
elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc.
FeS2, Iron Sulfide
Minerals
Non silicates:
•
•
•
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Sulphides
The mineral pyrite (FeS2) is the only sulphide that occurs commonly in rocks.
Sulphides are most important as economic minerals providing the main sources of
elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc.
Galena, Chalcopyrite
Minerals
Non silicates:
•
•
Phosphates are relatively rare. The only important phosphate mineral is apatite.
Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate
Common minerals
• the most common minerals you'll find in rocks (rock
forming minerals)
• This pile contains plagioclase feldspar, potassium feldspar,
quartz, muscovite mica, biotite mica, amphibole, olivine, and
calcite.
Acknowledged sources
1.www.specialconnections.k
u.edu/.../cs/.../caseb_rocks
_minerals.ppt –
2.www.earth2class.org/er/students/Mi
nerals.ppt
3.www.lwr.kth.se/Grundutbi
ldning/AE2401/.../review%2
0minerals.ppt
4.www.sci.uidaho.edu/geol1
11/Geology%20101/mineral
s_II_jh