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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?
• Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other
Physical Properties of Minerals
• 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
• Luster:– How a mineral surface reflects light
– Two major types:
• Metallic luster
• Non-metallic luster
Metallicexample:Galena
Non-metallicexample:
Orthoclase
Pyrite has metallic luster
Quartz has vitreous luster
Physical Properties of Minerals
• 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
• 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
• Cleavage is described by:– Number of planes– Angles between adjacent planes
– These are constant for a particular mineral
Physical Properties of Minerals
• Cleavage (1 direction):
Example: mica
Physical Properties of Minerals
• Cleavage (2 directions):
orthoclase
amphibole
Physical Properties of Minerals
• Cleavage (3 directions):
halite
calcite
Physical Properties of Minerals
• Cleavage (4 directions):
fluorite
Physical Properties of Minerals
• 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
• 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
GalenaSG=7.5
QuartzSG=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 MINERAL SPECIFIC GRAVITY
Framework Silicate Quartz 2.6-2.7
Framework Silicate Feldspar 2.6-2.7
Sheet Silicate Mica 2.8-3.0
Chain Silicate Amphibole 2.9-3.2
Chain Silicate Pyroxene 3.2-3.6
Isolated Silicate Olivine 3.3-4.4
Isolated Silicate Garnet 3.5-4.4
Sulphide Sphalerite 4.0
Sulphide Chalcopyrite 4.2
Sulphide Pyrite 5.0
Oxide Magnetite 5.2
Oxide Hematite 5.3
Sulphide Galena 7.2
Oxide Pitchblende 9.5
Element Native Gold 12.4
– reaction with hydrochloric acid (calcite fizzes)
Physical Properties of Minerals
• Other properties:
– taste (halite tastes salty)
– feel (talc feels soapy, graphite feels greasy)
– magnetism (magnetite attracts a magnet)
• 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
Mineral Groups
All others: 1.5%
Element Abundances
SilicaSilica(SiO(SiO44))4-4-SILICATES
Common cations thatbond with silica anions
mineral formula cleavage Silicate structureOlivine (MgFe)2SiO4 none Single
tetrahedronPyroxene (Mg, Fe) SiO3 two cleavage
planes at 900
chains
Amphiboles:Eg. hornblende
(Ca2Mg5)Si8O22(OH)2 Two planes at 600and 1200
Double chains
Mica Muscovite
KAl3Si3O10(OH)2 One plane sheets
Biotite K(MgFe)3Si3O10(OH)2
Feldspars:K-feldsparOrthoclase, microcline
KAlSi3O8 Two planes at 900 Three dimensional networks
Plagioclase (Ca,Na)AlSi3O8
Quartz SiO2 none Three dimensional network
Common Silicate mineral groups
group member formula usesOxides
Sulphides
Sulfates
Native elements
Halides
Carbonates
MagnetiteHaematiteCorundum
GalenaSphaleritePyrite
GypsumAnhydrite
GoldSilverCopperSulfurGraphite
HaliteFlourite
Calcite
Fe3O4
Fe2O3
Al2O3
PbSZnSFeS2
CaSO4.H2OCaSO4
AuAgCuSC
NaClCaF2
CaCO3
Ore of ironOre of ironAbrasive
Ore of leadOre of zincFool’s gold
Used for plaster
Precious metalPrecious metalUsed for WiresUsed in chemicalspencils
Common saltUsed in chemicals
Used in cement
Common Non Silicate mineral groups
– Oxides O2-
– Carbonates (CO3)2-
– Sulfides S2-
– Sulfates (SO4)2-
– Halides Cl-, F-, Br-
– Native elements (single elements; e.g., Au)
Mineral Groups
• Silicates (most abundant)
• Non-silicates (~8% of Earth’s crust):
Mineral Groups – Silicates
• Silicates– Tetrahedron
• fundamental building block
• 4 oxygen ions surrounding a much smaller silicon ion
Silicon-oxygentetrahedron
(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 –
Olivine Groupdark silicates (Fe-Mg)
Mineral Groups – Silicates
No cleavage
ferromagnesian
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.
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
Composition
Color Olive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, white
Streak Colorless
Hardness 6½ - 7
Crystal Formsand Aggregates
Usually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses.
Transparency Transparent to translucent
Specific Gravity 3.2 - 4.2
Luster Vitreous
Cleavage none
Fracture Conchoidal
Tenacity Brittle
Uses 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.
Striking Features Color, localities, and hardness
Complex Tests Soluble in hydrochloric acid
Pyroxene GroupFerromagnesian / dark silicates (Fe-Mg)
Mineral Groups – Silicates
2-directionsof cleavage(at nearly 90 degrees)
Augite
MineralsThe 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 MonoclinicLuster: Glassy or metallic Color: Black Streak: White, light green or light brown Hardness: 5-6.5 on Mohs hardness scaleCleavage: Two planes that meet at nearly a 90-degree angle Fracture: Most have uneven and brittle fractures.
Amphibole GroupFerromagnesian / dark silicates (Ca, Fe-Mg)
Mineral Groups – Silicates
2-directionsof cleavage(not at 90 degrees)
Hornblende
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 milkyColor: Black or dark green, translucent to opaqueStreak: Grey-green or grey-brownHardness: 5-6Cleavage: Two planes that meet at a 124-degree angleFracture: Uneven brittle fracture
Mica Group and Clay Mineralslight silicates (K, Al)
Mineral Groups – Silicates
1-directionof cleavage
Muscovite
non-ferromagnesian
Minerals• Micas and Clay Minerals
• Sheets of tetrahedra are the building blocks. Aluminum is also involved in thesesheet structures which are charge-balanced 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.
BiotiteK(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.
MuscoviteKAl3Si3O10 (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.
Feldspar Grouplight silicates (K-Na-Ca, Al)
Mineral Groups – Silicates
2-directionsof cleavage
(at 90 degrees)
Orthoclase
Plagioclase
K-feldspar
Ca/Na-feldspar
Most common mineral group
Minerals• Feldspar group
• A second group of alumino-silicates, 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
Quartzlight silicates (pure SiO2)
Mineral Groups – Silicates
no cleavage(conchoidal fracture)
hard, resistant to weatheringQuartz
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.QuartzShape: 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: vitreousColor: Colorless or white. Some varieties are pink or smoky. Streak: White Hardness: 7Cleavage: None Fracture: Conchoidal
Minerals• Quartz
• Silica tetrahedra alone can form a neutral three-dimensional 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
FerromagnesianSilicates (Fe, Mg)
Non-ferromagnesianSilicates (K, Na, Ca, Al)
OxidesCarbonatesSulfides/sulfatesNative elements
MineralsThere 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
Non silicates:
• Carbonates Co3
• The important carbonates are the minerals calcite and dolomite. Both are significant rock-forming minerals.
• The calcite group
• Calcite (Calcium Carbonate)
• Magnesite(Magnesium Carbonate)
• Rhodochrosite (Manganese Carbonate)
• Siderite(Iron Carbonate)
• Smithsonite (Zinc Carbonate)
Minerals
MineralsNon 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
MineralsNon silicates:
• Evaporites
•Fluorite: CaF2, Calcium Fluoride
MineralsNon silicates:
•Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate
MineralsNon silicates:
• Oxides
• oxides (hematite and magnetite) Fe2O3, Iron Oxide
• 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.
MineralsNon silicates:
• 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
MineralsNon silicates:
• 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
MineralsNon 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.
2.www.earth2class.org/er/students/Minerals.ppt
1.www.specialconnections.ku.edu/.../cs/.../caseb_rocks_minerals.ppt –
3.www.lwr.kth.se/Grundutbildning/AE2401/.../review%20minerals.ppt
4.www.sci.uidaho.edu/geol111/Geology%20101/minerals_II_jh
Acknowledged sources