Class Web site
http://geology.um.edu.my/iskandar/SGES1273/
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Classification of minerals
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According to characteristics
 E.g. Minerals with metallic luster, Green minerals,
minerals with cleavage, etc.
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Why classify
minerals?
According
to crystal shape
 E.g. Cubic minerals.
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According to chemistry
 E.g. Minerals containing Si.
Classifying minerals
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Dana’s Classification System
http://www.webmineral.com/danaclass.shtml
 Based on chemical composition and structure
Classifying minerals
Biggest group of minerals: silicates
 Non-silicates:
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Native elements
Halides
Carbonates, Nitrates, Borates
Sufates, Chromates, Molybdenates
Phosphates, Arsenates, Vanadates
– “Ore minerals”:
 Sulfides
 Oxides/hydroxides
Today
SiO2 minerals (i.e. quartz/chalcedony)
 Corundum (Al2O3)
 Carbonates
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 Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),
Siderite (FeCO3)
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Halides (salts)
 Halite (NaCl), Fluorite (CaF2)
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Phosphates
 Apatite Ca5(PO4)3(OH,F,Cl)
Quartz (SiO2)
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Color: Variable. Clear, purple, pink, etc.
Transparency: Crystals are transparent to translucent,
cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2.
Crystal Habits: Widely variable. Look for characteristic
crystal shape (hexagonal crystals with a six sided pyramid
termination). Cryptocrystalline or massive forms may be
botryoidal, globular, stalactitic, etc.
Cleavage: very weak in three directions rhombohedral).
Fracture: conchoidal
Hardness: 7, less in cryptocrystalline forms.
Specific Gravity: 2.65 or less if cryptocrystalline.
Streak: white.
http://mineral.galleries.com/minerals/silicate/quartz/quartz.htm
Quartz SiO2
Clear Quartz
Smoky Quartz
Rose Quartz
Amethyst
Cryptocrystalline Quartz SiO2
Chert/Agate/Chalcedony
Quartz (SiO2)
Diagnostic features
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Very common.
Transparency: Usually more transparent than
feldspar.
To tell apart from calcite (esp.
cryptocrystalline forms): No reaction with
acid.
Crystal Habits: Crystals have characteristic
shape.
Fracture: conchoidal. Usually no cleavage.
Hardness: 7, less in cryptocrystalline forms.
Harder than feldspar, calcite.
http://mineral.galleries.com/minerals/silicate/quartz/quartz.htm
Corundum (Al2O3)
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Color: Highly variable. White or colorless, blue, red,
yellow, green, brown, purple, and pink; samples can have
color zonation.
Luster: Vitreous to adamantine.
Transparency: Transparent to translucent.
Crystal System: Trigonal; bar 3 2/m
Crystal Habits: Sapphire crystals - six-sided barrel
shaped. Ruby - hexagonal prisms and blades.
Cleavage: None.
Fracture: Conchoidal.
Hardness: 9
Specific Gravity: Approximately 4.0+ (above average
for translucent minerals)
Streak: White, harder than streak plate.
http://mineral.galleries.com/minerals/oxides/corundum/corundum.htm
Corundum (Al2O3)
http://mineral.galleries.com/minerals/oxides/corundum/corundum.htm
Corundum (Al2O3)
Diagnostic features
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RARE
Luster: Vitreous to adamantine.
Transparency: Transparent to translucent.
Crystal Habits: Sapphire crystals - six-sided
barrel shaped. Ruby - hexagonal prisms and
blades.
Cleavage: None.
Fracture: Conchoidal.
Hardness: 9 (Harder than quartz)
Specific Gravity: Approximately 4.0+ (above
average for translucent minerals)
http://mineral.galleries.com/minerals/oxides/corundum/corundum.htm
SiO2 minerals (i.e. quartz/chalcedony)
 Corundum (Al2O3)
 Carbonates
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 Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),
Siderite (FeCO3)
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Halides (salts)
 Halite (NaCl), Fluorite (CaF2)
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Phosphates
 Apatite Ca5(PO4)3(OH,F,Cl)
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Carbonates
 Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),
Siderite (FeCO3)
ACID
CaCO3 + 2HCl  CaCl2 + H2O+
CO2
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Calcite, Aragonite -> Strong reaction to cold acid
Dolomite, Siderite -> Weak reaction to acid
Calcite (CaCO3)
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Color: extremely variable but generally white or colorless or with
light shades of yellow, orange, blue, pink, red, brown, green, black
and gray.
Luster: Vitreous to resinous to dull in massive forms.
Transparency: Crystals are transparent to translucent.
Crystal System: Trigonal; bar 3 2/m
Crystal Habits: See web site for many crystalline forms. Also
massive, fibrous, concretionary, stalactitic, nodular, oolitic, stellate,
dendritic, granular, layered, etc. etc.
Cleavage: Perfect in three directions, forming rhombohedrons.
Hardness is 3 (only on the basal pinacoidal faces, calcite has a
hardness of less than 2.5 and can be scratched by a fingernail).
Specific Gravity is approximately 2.7 (average)
Streak is white.
Reacts vigorously with acid.
http://mineral.galleries.com/minerals/carbonat/calcite/calcite.htm
Calcite (CaCO3)
Diagnostic features
Very common
 Reacts vigorously with acid.
 Cleavage: Perfect in three directions,
forming rhombohedrons.
 Hardness: 3 (soft)
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http://mineral.galleries.com/minerals/carbonat/calcite/calcite.htm
Calcite (CaCO3)
http://mineral.galleries.com/minerals/carbonat/calcite/calcite.htm
Aragonite (CaCO3)
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Color: White or colorless or with usually subdued shades of red,
yellow, orange, brown, green and even blue.
Luster: Vitreous to dull.
Transparency: Crystals are transparent to translucent.
Crystal System: Orthorhombic; 2/m 2/m 2/m
Crystal Habits: Hexagonal, often thin elongated prismatic, curved
bladed, steep pyramidal (spiked) and chisel shaped crystals. Can also
be compact, granular, radially fibrous and massive. Its massive forms
can be layered, coralloid, pisolitic, oolitic, globular, stalachtitic and
encrusting. The shells of many species are made up of aragonite.
Cleavage: Distinct in one direction (pinacoidal).
Hardness: 3.5 - 4 (harder than calcite)
Specific Gravity: 2.9+ (average for non-metallic minerals)
Streak: is white.
Reacts vigorously with acid.
Best Field Indicators are crystal habits, single plane of cleavage
and reaction to acid.
http://mineral.galleries.com/minerals/carbonat/aragonit/aragonit.htm
Aragonite (CaCO3)
Diagnostic features
Reacts vigorously with acid.
 Color: White or colorless or with usually subdued shades
of red, yellow, orange, brown, green and even blue.
 Crystal Habits: Easily confused with calcite, and is often
replaced by it in nature. Look for acicular or fibrous
habits. Also, coral skeletons, shells, tests, etc. are
deposited as aragonite (though they may later be altered
to calcite). Massive forms may be indistinguishable from
calcite.
 Cleavage: Distinct in one direction (pinacoidal). Calcite
cleaves in three directions.
 Hardness: 3.5 - 4 (harder than calcite)
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http://mineral.galleries.com/minerals/carbonat/aragonit/aragonit.htm
Aragonite (CaCO3)
http://mineral.galleries.com/minerals/carbonat/aragonit/aragonit.htm
Dolomite (CaMg(CO3) 2)
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Color: Pink or pinkish and can be colorless, white, yellow, gray or
even brown or black when iron is present in the crystal.
Luster: pearly to vitreous to dull.
Transparency: crystals are transparent to translucent.
Crystal System: trigonal; bar 3
Crystal Habits: saddle shaped rhombohedral twins and simple
rhombs some with slightly curved faces, also prismatic, massive,
granular and rock forming. Never found in scalenohedrons.
Cleavage: perfect in three directions forming rhombohedrons.
Fracture: conchoidal.
Hardness: 3.5-4
Specific Gravity: 2.86
Streak: white.
Reacts weakly with acid.
http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm
Dolomite (CaMg(CO3) 2)
Diagnostic features
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Reacts weakly with acid. Use this test to differentiate it
from Calcite and Aragonite.
Color: often pink or pinkish and can be colorless, white,
yellow, gray or even brown or black when iron is present in
the crystal.
Luster: pearly to vitreous to dull.
Crystal Habits: Most commonly massive, looks very much
like calcite.
Cleavage: perfect in three directions forming
rhombohedrons (just like calcite).
Fracture: conchoidal.
Hardness: 3.5-4 (harder than calcite)
http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm
Dolomite (CaMg(CO3) 2)
http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm
Siderite (FeCO3)
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Color: Yellowish brown, brown, gray, yellowish gray, or greenish
gray.
Luster: Vitreous to pearly
Transparency: Translucent to subtranslucent
Crystal System: Trigonal; bar 3 2/m
Crystal Habits: Tabular, massive, botryoidal are found.
Cleavage: perfect in three directions forming rhombohedrons.
Fracture: Conchoidal. Very brittle fracture producing small,
conchoidal fragments
Hardness: 3.5
Specific Gravity: 3.96 (denser than calcite and dolomite)
Streak: white.
Reacts weakly with acid.
http://mineral.galleries.com/minerals/carbonat/siderite/siderite.htm
Siderite (FeCO3)
Diagnostic features
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Reacts weakly with acid (like dolomite)
Specific Gravity: 3.96 (use this to distinguish
siderite from dolomite)
Color: Variable – Yellowish, brown, grey.
Crystal Habits: Most commonly massive, looks
very much like calcite.
Cleavage: perfect in three directions forming
rhombohedrons (like calcite).
Fracture: conchoidal.
Hardness: 3.5 (harder than calcite)
http://mineral.galleries.com/minerals/carbonat/siderite/siderite.htm
Siderite (FeCO3)
http://mineral.galleries.com/minerals/carbonat/siderite/siderite.htm
SiO2 minerals (i.e. quartz/chalcedony)
 Corundum (Al2O3)
 Carbonates
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 Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),
Siderite (FeCO3)
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Halides (salts)
 Halite (NaCl), Fluorite (CaF2)
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Phosphates
 Apatite Ca5(PO4)3(OH,F,Cl)
Halite (NaCl)
Color: Clear or white but sometimes blue, purple, pink,
yellow and gray.
 Luster: Vitreous.
 Transparency: Transparent to translucent.
 Crystal System: Isometric; 4/m bar 3 2/m
 Crystal Habits: Predominantly cubes and in massive
sedimentary beds, but granular, fibrous and compact
forms exist. Some crystals show a crystal type called a
hopper crystal.
 Cleavage: Perfect in three directions forming cubes.
 Fracture is conchoidal.
 Hardness: 2 (softer than calcite)
 Specific Gravity: 2.1+ (light)
 Streak:White.
 Taste: Salty
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http://mineral.galleries.com/minerals/halides/halite/halite.htm
Halite (NaCl)
Diagnostic features
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Taste: Salty
Transparency: Transparent to translucent.
Crystal Habits: Look for cubic crystals or
fragments
Cleavage: Perfect in three directions forming
cubes.
Fracture is conchoidal.
Hardness: 2 (softer than calcite)
Specific Gravity: 2.1+ (light)
Streak:White.
http://mineral.galleries.com/minerals/halides/halite/halite.htm
Halite (NaCl)
http://mineral.galleries.com/minerals/halides/halite/halite.htm
Fluorite CaF2
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Color: Extremely variable. Can be an intense purple, blue, green or
yellow; also colorless, reddish orange, pink, white and brown. A
single crystal can be multi-colored. But most often purple.
Luster: Vitreous.
Transparency: Transparent to translucent.
Crystal System: Isometric; 4/m bar 3 2/m
Crystal Habits: Very often found as crystals with free faces, in veins
and geodes. Crystals are typically cubes, to a lesser extent,
octahedra. Also other rarer isometric habits. Always with equant
crystals; less common are crusts and botryoidal forms. Twinning also
produces penetration twins that look like two cubes grown together.
Cleavage: Perfect in 4 directions forming octahedrons.
Fracture: Irregular and brittle.
Hardness: 4 (Softer than quartz)
Specific Gravity: 3.1+ (average)
Streak: is white.
http://mineral.galleries.com/minerals/halides/fluorite/fluorite.htm
Fluorite (CaF2)
Diagnostic features
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Color: Most often purple, but this is not a reliable
diagnostic feature as color can vary widely.
Transparency: Transparent to translucent.
Crystal System: Isometric; 4/m bar 3 2/m
Crystal Habits: Look for cubic and octahedral crystals,
but also found in other forms such as crusts and
botryoidal masses.
Cleavage: Perfect in 4 directions forming octahedrons.
Hardness: 4 (Softer than quartz)
Differentiate from quartz – hardness
Differentiate from calcite – no acid reaction
http://mineral.galleries.com/minerals/halides/halite/halite.htm
Fluorite (CaF2)
http://mineral.galleries.com/minerals/halides/fluorite/fluorite.htm
SiO2 minerals (i.e. quartz/chalcedony)
 Corundum (Al2O3)
 Carbonates
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 Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),
Siderite (FeCO3)
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Halides (salts)
 Halite (NaCl), Fluorite (CaF2)
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Phosphates
 Apatite Ca5(PO4)3(OH,F,Cl)
Apatite (Ca5(PO4)3(OH,F,Cl))
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Color: Typically green but also yellow, blue, reddish brown and purple.
Luster: Vitreous to greasy and gumdrop.
Transparency: Transparent to translucent.
Crystal System: Hexagonal; 6/m
Crystal Habits: Typically a hexagonal prism with the hexagonal pyramid or
a pinacoid or both as a termination. Also accicular, granular, reniform and
massive. A cryptocrystalline variety is called collophane and can make up a
rock type called phosphorite and also can replace fossil fragments.
Cleavage: Indistinct in one basal direction.
Fracture: Conchoidal.
Hardness: 5 (softer than quartz).
Specific Gravity: Approximately 3.1 - 3.2 (average for translucent minerals)
Streak: White.
Other Characteristics: An unusual "partially dissolved" look similar to the
look of previously sucked on hard candy.
http://mineral.galleries.com/minerals/phosphat/apatite/apatite.htm
Apatite (Ca5(PO4)3(OH,F,Cl))
Diagnostic features
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Color: Typically green but also yellow, blue, reddish brown
and purple.
Luster: Vitreous to greasy and gumdrop.
Transparency: Transparent to translucent.
Crystal Habits: Usually long, hexagonal prismatic crystals.
Cleavage: Indistinct in one basal direction.
Fracture: Conchoidal.
Hardness: 5 (softer than quartz).
Other Characteristics: An unusual "partially dissolved"
look similar to the look of previously sucked on hard candy.
Differentiate from Corundum - hardness
http://mineral.galleries.com/minerals/phosphat/apatite/apatite.htm
Apatite (Ca5(PO4)3(OH,F,Cl))
http://mineral.galleries.com/minerals/phosphat/apatite/apatite.htm