mineral

Classifying minerals

• Biggest group of minerals: silicates• Non-silicates:

• 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 • Calcite, Aragonite (CaCO)3, Dolomite (CaMg(CO3)2),

Siderite (FeCO3)

• Halides (salts)• Halite (NaCl), Fluorite (CaF2)

• Phosphates• Apatite Ca5(PO4)3(OH,F,Cl)

Quartz (SiO2)• 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

Amethyst

Smoky Quartz

Rose Quartz

Cryptocrystalline Quartz SiO2

Chert/Agate/Chalcedony

Quartz (SiO2)Diagnostic features

• 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.

Corundum (Al2O3)• 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.

Corundum (Al2O3)

Corundum (Al2O3)Diagnostic features

• 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)



• Carbonates • Calcite, Aragonite (CaCO3, Dolomite (CaMg(CO3)2),

Siderite (FeCO3)




Siderite (FeCO3)

ACID

CaCO3 + 2HCl CaCl2 + H2O+ CO2

• Calcite, Aragonite -> Strong reaction to cold acid• Dolomite, Siderite -> Weak reaction to acid

Calcite (CaCO3)• 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.

Calcite (CaCO3)Diagnostic features

• Very common• Reacts vigorously with acid. • Cleavage: Perfect in three directions, forming

rhombohedrons. • Hardness: 3 (soft)

Calcite (CaCO3)

Aragonite (CaCO3)• 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.

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)

Aragonite (CaCO3)

Dolomite (CaMg(CO3) 2)

• 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.

Dolomite (CaMg(CO3) 2) Diagnostic features

• 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)

Dolomite (CaMg(CO3) 2)

Siderite (FeCO3)

• 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.

Siderite (FeCO3) Diagnostic features

• 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)

Siderite (FeCO3)

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

Halite (NaCl)Diagnostic features

• 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.

Halite (NaCl)

Fluorite CaF2

• 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/property/twins.htm

Fluorite (CaF2) Diagnostic features

• 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

Fluorite (CaF2)




Siderite (FeCO3)



Apatite (Ca5(PO4)3(OH,F,Cl))• 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.

Apatite (Ca5(PO4)3(OH,F,Cl))Diagnostic features

• 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

Apatite (Ca5(PO4)3(OH,F,Cl))

mineral

Documents

crystal habits

cryptocrystalline forms

crystal system

translucent minerals

massive forms

sapphire crystals

conchoidal hardness

aragonite caco3