NAME
FORMULA
Calcite
CaCO3
HABIT
LUSTRE
S.g.
vitreous
2.7
USUAL COLOUR/
STREAK
colourless or
white
white
HARDNESS
CLEAVAGE
3
3 perfect,
rhombohedral
tabular habit
vitreous
2.3
Satin spar gypsum
fibrous
vitreous
2.3
clear,
colorless,
white, gray,
yellow, red,
brown
White
colourless, white
white
Halite (rock salt)
NaCl
cubic crystals, with
hollow stepped faces
vitreous
2.2
colourless, white
white
2 - 2.5
3 good, cubic
Tastes of salt, soluble in
water (so clean it in petrol)
evaporite, playa lake deposit food
processing, washing soda
Quartz
SiO2
elongatedhexagonal
prisms capped by
pyramids,or crystalline
granular
vitreous
2.65
colourless in rock
crystal - see
guide to
properties for
other varieties
white
7
Conchiodal
fracture
horizontal striations on
crystal faces, conchoidal
fracture
as sand and sandstone,in veins, as
geodes, constituent in many igneous
and metamorphic rocks microchips,
gemstone. concrete and glass making
(as sand)
Biotite mica
foliaceous, platey,
pseudo-hexagonal
crystals
pearly
3.0
brown, black
white
2.5 - 3
1 perfect basal
Limonite
iron-bearing deposits
Earthy
Light brown to
brown, may be
yellowish-brown
Yellowish brown
to red
copper red on a
fresh surface,
dull brown on a
tarnished
surface
metallic copper
red
White, yellow,
green, gray,
brown, black,
purple;
sometimes
multicolored
White
4 - 5.5
Earthy
rhombohedral, dog
tooth and nail head
crystals
ousAlabaster
Gypsum
FeO(OH) ·
nH
2O
2.7 - 4.3
Copper
Metallic
8.9
Serpentine
(Asbestos)
Greasy, waxy, or
silky
2.5 – 3.2
OTHER PROPERTIES
OCCURRENCE USES
effervesces vigorously in dil.
HCl. double refraction of
images viewed throught it
2
1 perfect, parallel
to crystal faces
as limestone, in veins, as stalactites,
stalagmites
lime fertilizer, cement, flux in steel
industry
evaporites and free-growing in clays
plaster-of-paris, plasterboard ie.
Gyproc
2
n/a
evaporites plaster-of-paris,
plasterboard i.e.. Gyproc
a common rock forming mineral in
sedimentary, metamorphic and
igneous rocks used for furnace
windows heat resistant formica and
as glitter in a wide range of products.
2.5 – 3
None
2.5
Fibrous Fracture
excellent conductor of electricity,
mostly as wiring
Greasy Feel
NAME
FORMULA
Muscovite mica
K2Al4
[Si6Al2O20]
(OH,F)4
HABIT
LUSTRE
S.g.
pearly
3.0
USUAL COLOUR/
STREAK
silvery-white
(named after
Moscow in
'White Russia'
white
HARDNESS
CLEAVAGE
2 - 2.5
1 perfect basal
Fluorite,
cubic crystals or as
crystalline masses
vitreous,
sometimes a very
slightly greasy or
watery
appearance
2.7
colourless, blue&
yellow as blue
john variety
white
4
4 perfect
octahedral:cleavage planes
cut across
corners of 6sided cubic
crystals to leave
8-sided
octahedral cores.
Orthoclase
feldspar
(complex
framework
silicate)
prismatic, tabular or
rectangular crystals
vitreous to pearly
about 2.6
colourless (may
be cloudy),
white, pink or
pale red, other
pale colours also
white
6 (a moh's scale
mineral)
2 cleavages at 90
degrees
foliaceous, platey,
pseudo hexagonal
crystals
Calcium rich
Plagioclase
feldspar
(complex
framework
silicate)
OCCURRENCE USES
a common rock forming mineral in
sedimentary, metamorphic and
igneous rocks
used for furnace windows heat
resistant formica and as glitter in a
wide range of products.
vein mineral
semi-precious gemstone as blue
john (from French; bleu-blue
jaune-yellow). Also used as flux in
steel smelting
sub-transparent to
translucent
orthoclase is named after
its 2 cleavages at right
angles:
common rock forming mineral in
igneous, metamorphic and
sedimentary rocks
used in vitreous chinaware and as
an abrasive in scouring powders.
ortho=right
klastos=breaks,
prismatic, tabular or
rectangular crystals
vitreous to pearly
about 2.7
white or grey to
grey-blue or
other pale
colours
white
6 - 6.5
2 cleavages at
almost 90
degrees
Potassium Rich
sub-transparent to
translucent
plagioclase is named after
its 2 cleavages at almost
right angles:
common rock forming mineral in
igneous, metamorphic and
sedimentary rocks
used in vitreous chinaware and as
an abrasive in scouring powders.
plagio=almost
klastos=breaks
Magnetite
Apatite
OTHER PROPERTIES
Hexagonal crystal
form
Metallic
5.18
Black metallic
Black or silver
6
Uneven
Vitreous
3.1 - 3.2
Green or Red
White
5.0
Poor
Strongly Magnetic
manufacture of fertilizer - it is a
source of phosphorus
NAME
FORMULA
Talc
HABIT
Olivine
FeMgSiO4
tabular crystals or
granular crystalline asses
vitreous
2.5 - 3.5
(more
often ~3.5)
Garnet
(a group of
Fe,Ca,Al,Cr,
Mn & Mg,
silicate
minerals)
rhombo-dodecahedral,
dodecahedral and tetrahexahedral crystals, also
as angular fragments
Malachite
Cu2[(OH)
2CO3]
crypto-crystalline
Sulfur
Galena
PbS
cubic crystals
LUSTRE
S.g.
Pearly
2.7 - 2.8
USUAL COLOUR/
STREAK
green, white,
gray, brown,
colorless
white to pale
green
green, may also
be yellow or
brown
white
HARDNESS
CLEAVAGE
1
Earthy fracture
vitreous
3.6 - 4.3
deep red,
crimson, purple,
brown, black,
olive, greens,
pink, yellow
white
no cleavage
7 - 7.5 (except
gossular variety,
which may be as
low as 6.5)
a dense mineral formed in high
pressure/temperature condition in
metamorphic rocks
used as a gemstone and as an
abrasive (garnet paper is a red
abrasive paper used on wood).
dull
4.0
emerald green,
or other shades
of green
light green,
4.0
a weathering product of copper
deposits
Vitreous,
Resinous Greasy
2.0 - 2.1
Lemon Yellow
Yellow
1.5 – 2.5
Conchoidal fracture
metallic
7.5
silver-grey
grey-black
2.5
3; perfect
cubic cleavage
Waxy
2.15
Colorless, white,
yellow, red,
orange, green,
brown, black,
blue
White
5.5 – 6.5
Dull
3.8 -4
Blue
Pale Blue
3.5 – 4
Conchoidal or
splintery fracture
Opal
Azurite
OTHER PROPERTIES
OCCURRENCE USES
Greasy /soapy feel
been used to make ornamental and
practical objects for thousands of
years. Important ingredient in many
baby powders, foot powders, first aid
powders and a variety of cosmetics.
occurs in basic and ultrabasic igneous
rock, best crystals occur in olivineperidotite
gemstone
1 poor cleavage,
cracks on what
appears to be
second cleavage
plane; actually a
sub-parallel fracture
6-7
odor (see above), poor heat
conductivity makes it brittle
when heated and can
actually crack if held tightly
in a person's hand
vein mineral, often with calcite,
fluorspar and barites
cheif source of lead (Pb).
Conchoidal fracture
minor ore of copper, gemstone,
ornamental stone
NAME
FORMULA
Haematite
Fe2O3
Pyrite
FeS2
Sphalerite
(aka zinc blende,
black jack)
ZnS
HABIT
reniform aggregate habit
cubic crystals, or as
pentagonal
dodecahedral crystals.
Also as nodules with an
internal structure of
radiating needles, also
as crystalline masses
usually massive
aggregates, also
tetrahedral crystals
LUSTRE
S.g.
earthy
5
USUAL COLOUR/
STREAK
Red-brown
red-brown
brass-yellow
black
6 - 6.5
no cleavage
resinous,
sometimes
brilliant or
adamantine on
fresh surfaces
4.0
brown or black
pale yellow
3.5 - 4
perfect
cleavage in 6
directions
White
White
Kaolinite
Dull,
Earthy
2.6
White to
cream
White
Obsidian
Vitreous
2.3 - 3
Black
3.5 – 4
Uneven
fracture
2 – 2.5
OTHER PROPERTIES
sub-conchoidal or uneven
fracture
cubic crystals often have
striated faces, conchoidal
fracture,
sparks when struck with
geological hammer pyrite =
fire mineral.
smells sulphurous when
rubbed on a streak plate
smells sulphurous when
rubbed on a streak plate
Black to dark
green
Brown to grey
6
imperfect in
two directions
at 56 and 124
degrees
Waxy, Dull
2.59 - 2.61
colorless,
white, gray,
blue, any color
due to
embedded
minerals,
White
6.5 – 7
Conchoidal
Fracture
OCCURRENCE USES
often in limestones as a relacement
minerals, also in metamorfphic
deposites, ironstones and as both
thin veins and cement in sandstones
eg. the New Red Sandstone
iron ore and used as a pigment
in paint 'Red Ochre'
occurs as free crystals or nodules in
coal, clay and shales, also in veins
formerly source of sulphur,
used to make sulphuric acid
(native sulphur now main
source).
vein mineral
chief source of [non-corrosive]
zinc, used for galvanisation of
iron
Clay like properties
when water is added
5 – 5.5
Conchoidal
Fracture
Vitreous
2.9 - 3.4
Hornblende
Chalcedony
5.5 to 6.5
2 poor
cleavages
metallic
5.0
Pearly
2.2
Stilibite
HARDNESS
CLEAVAGE
naturally occurring volcanic
glass formed as an extrusive
igneous rock
Large crystals have an
almost striated or grainy
appearance.