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QUARTZ
chemical composition
*
form
Hexagonal prisms
habit
Prismatic and massive most common
twinning
Not uncommon
colour
*
hardness
*
occurrence
cleavage
Essential in acid igneous rocks. Large crystals
in pegmatites. Common detrital mineral in
sedimentary rocks.
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
cleavage
Important constituent of limestones. Can form
in veins from fluids.
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.
L.Blair 2005
OLIVINE
chemical composition
(Mg, Fe)2SiO4 (magnesium iron silicate)
form
-
habit
Tabular/box-shaped crystals (rare)
twinning
Rare
colour
*
hardness
6.5 - 7
occurrence
cleavage
Essential in ultrabasic igneous rocks and some
marbles. Also found in iron-nickel meteorites.
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
fracture
Essential mineral in acidic igneous rocks. In
some metamorphic and sedimentary rocks.
Good in 2 directions forming nearly right-angled
prisms.
Conchoidal or uneven.
density (g/cm3)
2.5
streak
*
lustre
Vitreous (dull if weathered)
transparency
*
reaction with cold dilute HCl
No reaction
cleavage
other features/points of interest
L.Blair 2005
PLAGIOCLASE FELDSPAR
chemical composition
form
(Na,Ca)Al1-2Si3-2O8 (sodium and/or calcium
aluminium silicate)
-
habit
Often flat or bladed
twinning
*
colour
*
hardness
6 – 6.5
occurrence
fracture
Found in igneous, sedimentary and
metamorphic rocks.
Perfect in 1 direction, good in another forming
nearly right-angled prisms.
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
cleavage
other features/points of interest
L.Blair 2005
AUGITE (in the pyroxene group of minerals)
chemical composition
(Ca, Na)(Mg, Fe, Al)(Al, Si)2 O6
form
-
habit
twinning
Usually short prismatic crystals with square
cross-section
?
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
twinning
Short, stocky prismatic crystals and long thin
crystals
?
colour
*
hardness
*
occurrence
cleavage
Important minerals in intermediate igneous
rocks.
*
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
L.Blair 2005
MICA
chemical composition
form
Potassium aluminum silicate hydroxide fluoride
(muscovite mica)
Potassium iron magnesium aluminum silicate
hydroxide (biotite mica)
-
habit
*
twinning
?
colour
*
hardness
*
occurrence
cleavage
Common in igneous, metamoprphic and detrital
sedimentary rocks
*
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
twinning
Variable. Includes massive, botryoidal, reniform
and bladed.
?
colour
*
hardness
5-6
occurrence
cleavage
Found in igneous, metamorphic and
sedimentary rocks (Banded Iron Formations)
Absent
fracture
Uneven
density (g/cm3)
5.3
streak
*
lustre
*
transparency
*
reaction with cold dilute HCl
No reaction
other features/points of interest
L.Blair 2005
GALENA
chemical composition
*
form
Cubic (including octahedrons)
habit
*
twinning
Common.
colour
*
hardness
*
occurrence
cleavage
Common in hydrothermal vein deposits. Also
occurs in massive sulphide beds.
*
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
twinning
Variable. Includes cubic crystals, nodules,
massive, reniform (also can replace fossils)
Common.
colour
*
hardness
6 – 6.5
occurrence
cleavage
Widespread. In igneous rocks, hydrothermal
veins, contact metamorphic rocks and
anaerobic sediments.
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
L.Blair 2005
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
Peacock Ore
FLUORITE
chemical composition
CaF2 (calcium fluoride)
form
Cubic
habit
*
twinning
Common
colour
*
hardness
*
occurrence
cleavage
Found in granites and pegmatites. Occurs as
hydrothermal deposits.
*
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
L.Blair 2005
BARITE
chemical composition
BaSO4 (barium sulphate)
form
-
habit
Commonly forms bladed or tabular crystals.
twinning
?
colour
*
hardness
3 – 3.5
occurrence
cleavage
Common in hydrothermal veins (occurs with
fluorite, calcite and quartz)
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
twinning
Often forms cubc crystals but can also be
massive, granular or fibrous.
?
colour
*
hardness
*
occurrence
cleavage
In evaporite deposits (from evaporated bodies
of saline water).
*
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!
L.Blair 2005
GYPSUM
chemical composition
CaSO4 · 2H2O (hydrated calcium sulphate)
form
-
habit
twinning
Variable. Tabular, bladed, massive, fibrous,
acicular etc. Also forms ‘desert roses’.
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: http://mineral.galleries.com
L.Blair 2005
http://www.minerals.net/mineral