QUARTZ

chemical composition / *
form / Hexagonal prisms
habit / Prismatic and massive most common
twinning / Not uncommon
colour / *
hardness / *
occurrence / Essential in acid igneous rocks. Large crystals in pegmatites. Common detrital mineral in sedimentary rocks.
cleavage / Poor (in 3 directions)
fracture / *
density (g/cm3) / 2.65
streak / white
lustre / *
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

CALCITE

chemical composition / *
form / Variable, often rhombohedrons.
habit / Variable. Massive, fibrous, prismatic etc.
twinning / Common.
colour / *
hardness / *
occurrence / Important constituent of limestones. Can form in veins from fluids.
cleavage / Perfect in 3 directions (forms rhombohedrons)
fracture / Conchoidal
density (g/cm3) / 2.7
streak / *
lustre / Vitreous to dull
transparency / *
reaction with cold dilute HCl / *
other features/points of interest / Double refraction.

OLIVINE

chemical composition / (Mg, Fe)2SiO4 (magnesium iron silicate)
form / -
habit / Tabular/box-shaped crystals (rare)
twinning / Rare
colour / *
hardness / 6.5 - 7
occurrence / Essential in ultrabasic igneous rocks and some marbles. Also found in iron-nickel meteorites.
cleavage / Poor
fracture / *
density (g/cm3) / 6.5 - 7
streak / *
lustre / *
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

ORTHOCLASE FELDSPAR (ALKALI FELDSPAR/K-FELDSPAR)

chemical composition / KAlSi3O8, (potassium aluminum silicate).
form / -
habit / Blocky or tabular crystals
twinning / Common
colour / *
hardness / *
occurrence / Essential mineral in acidic igneous rocks. In some metamorphic and sedimentary rocks.
cleavage / Good in 2 directions forming nearly right-angled prisms.
fracture / Conchoidal or uneven.
density (g/cm3) / 2.5
streak / *
lustre / Vitreous (dull if weathered)
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

PLAGIOCLASE FELDSPAR

chemical composition / (Na,Ca)Al1-2Si3-2O8 (sodium and/or calcium aluminium silicate)
form / -
habit / Often flat or bladed
twinning / *
colour / *
hardness / 6 – 6.5
occurrence / Found in igneous, sedimentary and metamorphic rocks.
cleavage / Perfect in 1 direction, good in another forming nearly right-angled prisms.
fracture / Conchoidal
density (g/cm3) / 2.6
streak / White
lustre / Vitreous (dull if weathered)
transparency / Transparent, translucent or opaque
reaction with cold dilute HCl / No reaction
other features/points of interest

AUGITE (in the pyroxene group of minerals)

chemical composition / (Ca, Na)(Mg, Fe, Al)(Al, Si)2 O6
form / -
habit / Usually short prismatic crystals with square cross-section
twinning / ?
colour / *
hardness / *
occurrence / Basic igneous rocks.
cleavage / *
fracture / Uneven
density (g/cm3) / 3.5
streak / *
lustre / Vitreous, submetallic or dull
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

HORNBLENDE (in the amphibole group of minerals)

chemical composition / Ca2(Mg, Fe, Al)5 (Al, Si)8O22(OH)2
form / -
habit / Short, stocky prismatic crystals and long thin crystals
twinning / ?
colour / *
hardness / *
occurrence / Important minerals in intermediate igneous rocks.
cleavage / *
fracture / Uneven
density (g/cm3) / 3
streak / White/grey/pale green?
lustre / Vitreous to dull
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

MICA

chemical composition / Potassium aluminum silicate hydroxide fluoride (muscovite mica)
Potassium iron magnesium aluminum silicate hydroxide (biotite mica)
form / -
habit / *
twinning / ?
colour / *
hardness / *
occurrence / Common in igneous, metamoprphic and detrital sedimentary rocks
cleavage / *
fracture / Not readily observed
density (g/cm3) / 2.5 - 3
streak / White
lustre / *
transparency / Transparent to translucent
reaction with cold dilute HCl / No reaction
other features/points of interest

HAEMATITE

chemical composition / *
form / -
habit / Variable. Includes massive, botryoidal, reniform and bladed.
twinning / ?
colour / *
hardness / 5 - 6
occurrence / Found in igneous, metamorphic and sedimentary rocks (Banded Iron Formations)
cleavage / Absent
fracture / Uneven
density (g/cm3) / 5.3
streak / *
lustre / *
transparency / *
reaction with cold dilute HCl / No reaction
other features/points of interest

GALENA

chemical composition / *
form / Cubic (including octahedrons)
habit / *
twinning / Common.
colour / *
hardness / *
occurrence / Common in hydrothermal vein deposits. Also occurs in massive sulphide beds.
cleavage / *
fracture / Uneven but rarely seen.
density (g/cm3) / *
streak / *
lustre / *
transparency / Opaque
reaction with cold dilute HCl / No reaction
other features/points of interest

PYRITE

chemical composition / *
form / Cubic (including octahedrons)
habit / Variable. Includes cubic crystals, nodules, massive, reniform (also can replace fossils)
twinning / Common.
colour / *
hardness / 6 – 6.5
occurrence / Widespread. In igneous rocks, hydrothermal veins, contact metamorphic rocks and anaerobic sediments.
cleavage / Poor
fracture / Conchoidal
density (g/cm3) / 5.1
streak / *
lustre / *
transparency / Opaque
reaction with cold dilute HCl / No reaction
other features/points of interest / Fool’s Gold

CHALCOPYRITE

chemical composition / CuFeS2 (copper iron sulphide)
form / -
habit / Usually massive but crystals may occur.
twinning / Not uncommon.
colour / *
hardness / 3.5 - 4
occurrence / Mainly found in hydrothermal veins.
cleavage / Poor in 1 direction.
fracture / Conchoidal
density (g/cm3) / 4.2
streak / *
lustre / *
transparency / Opaque
reaction with cold dilute HCl / No reaction
other features/points of interest / PeacockOre

FLUORITE

chemical composition / CaF2 (calcium fluoride)
form / Cubic
habit / *
twinning / Common
colour / *
hardness / *
occurrence / Found in granites and pegmatites. Occurs as hydrothermal deposits.
cleavage / *
fracture / Irregular and brittle
density (g/cm3) / 3.1
streak / *
lustre / *
transparency / Transparent to translucent
reaction with cold dilute HCl / No reaction
other features/points of interest

BARITE

chemical composition / BaSO4 (barium sulphate)
form / -
habit / Commonly forms bladed or tabular crystals.
twinning / ?
colour / *
hardness / 3 – 3.5
occurrence / Common in hydrothermal veins (occurs with fluorite, calcite and quartz)
cleavage / Perfect in 1 direction, poor in another
fracture / Conchoidal
density (g/cm3) / *
streak / *
lustre / *
transparency / Transparent to translucent
reaction with cold dilute HCl / No reaction
other features/points of interest

HALITE

chemical composition / *
form / Cubic
habit / Often forms cubc crystals but can also be massive, granular or fibrous.
twinning / ?
colour / *
hardness / *
occurrence / In evaporite deposits (from evaporated bodies of saline water).
cleavage / *
fracture / Conchoidal
density (g/cm3) / 2.1
streak / *
lustre / Vitreous
transparency / Transparent to translucent
reaction with cold dilute HCl / No reaction
other features/points of interest / Taste!

GYPSUM

chemical composition / CaSO4 · 2H2O (hydrated calcium sulphate)
form / -
habit / Variable. Tabular, bladed, massive, fibrous, acicular etc. Also forms ‘desert roses’.
twinning / Common (‘fish tail’ twins)
colour / *
hardness / *
occurrence / Common in evaporite deposits.
cleavage / Good in 1 direction, distinct in 2 others.
fracture / Uneven, rarely seen.
density (g/cm3) / 2.3
streak / *
lustre / *
transparency / Transparent to translucent.
reaction with cold dilute HCl / No reaction
other features/points of interest / Selenite refers to a transparent, colourless variety of gypsum.
Anhydrite is anhydrous calcium sulphate

Good mineral data:

L.Blair 2005