Geoscience Reference
In-Depth Information
Table A9.1
Continued
Mineral (abbreviation)
formula
Colour; lustre
Typical habit
Cleavage;
twinning
Hardness (H)
Cordierite (Crd)
(Mg,Fe)
2
A1
4
Si
5
O
18
Colourless, grey,
green, blue if fresh;
greasy to glassy
Indistinct ovoid
blobs or interstitial
grains
Poor cleavage
7
Chloritoid (Cld)
(Fe,Mg)A1
2
SiO
5
(OH)
2
Green to grey;
pearly
Elongate or stumpy
prisms
Poor cleavage;
multiple twins
6.5
Epidote (Ep)
Ca
2
(A1,Fe)
3
(SiO
4
)
3
(OH)
Pistachio-green;
glassy
Stumpy prisms or
groundmass
1 cleavage
6-7
Glaucophane (Gln)
Na
2
(Mg,Fe)
3
A1
2
Si
8
O
22
(OH)
2
Dark blue to black;
glassy to pearly
Elongate prisms
2 cleavages
intersect at 124°
and 56°
6-6.5
Pyroxene (Px)
(Ca,Na)(Mg,Fe)(Si,Al)
8
O
6
Green, brown,
black, bright green
(omphacite); glassy
Stocky prisms;
porphyroblasts
2 cleavages
intersect at 92°
and 88°
6
Hornblende (Hbl)
Ca
2
(Mg,Fe,Al)
5
(A1,Si)
8
O
22
(OH)
2
Green, black,
brown; more glassy
than most
pyroxenes
Stumpy or
elongate prisms;
porphyroblasts
2 cleavages
intersect at 124°
and 56°
5-6
Actinolite (Act)
Ca
2
(Mg,Fe)
5
Si
8
O
22
(OH)
2
Dark green; more
glassy than
pyroxenes
Slender prisms
2 cleavages
intersect at 124°
and 56°
5.5
Talc (Tlc)
Mg
3
Si
4
O
10
(OH)
2
White, pale green;
pearly
Soft fl akes; forms
scaly foliations
1 perfect
cleavage
1
Calcite (Cal)
CaCO
3
Colourless, white,
pink, yellow; glassy
Irregular,
interstitial grains
3 perfect
cleavages,
forming rhombs
3
Serpentine(Srp)
(Mg,Fe)
3
Si
2
O
5
(OH)
4
Green; silky
Fibrous masses
Usually not
visible (fi brous
crystals)
2.5
Tourmaline (Tur)
NaFe
3
A1
6
Si
6
O
18
(BO
3
)(OH)
4
Black, brown,
grey-blue; glassy
Slender prisms
with triangular
cross-sections
Poor cleavage
7.5
