Geoscience Reference
In-Depth Information
Table A6.2
Features of common minerals that constitute sedimentary deposits.
Mineral
Chemical
formula and
name
Colour in
hand
specimen
Cleavage
Other features
in hand
specimen
Form and
occurrence
Quartz
SiO
2
(silica)
Translucent
None
Will scratch steel
Common
detrital grain,
also a cement
Clay
minerals
Various hydrous
aluminosilicates
Typically grey,
green or red
Planar or
none
Fine-grained
Calcite
(sparite and
micrite)*
CaCO
3
(calcium
carbonate)
Translucent or
white; variety of
pale colours due
to impurities
Rhombic
Scratched by steel;
fresh surfaces fi zz
with acid
Forms grains,
matrix and
cement in
limestones,
dolomites and
sandstones
Aragonite
CaCO
3
(calcium
carbonate)
White with a
pearly
iridescence
Rectilinear
Original aragonitic
bioclasts are often
preserved in
marine mudrocks
Dolomite
CaMg(CO
3
)
2
(calcium
magnesium
carbonate)
Buff, cream
Rhombic
Fizzes with warm
acid and very
weakly with cold
acid
Feldspar
Various including
K(Na)AlSi
3
O
8
(orthoclase) and
Na(Ca) AlSi
3
O
8
(albite)
Transluscent or
pink or white
Present
Scratched by steel;
weathers to white,
powdery clay
minerals
Detrital
crystals
Glauconite
KMg(Fe,Al)
(SiO
3
)
6
.3H
2
O
Green
Planar
Soft; weathers to
the iron oxide
limonite
Ooids, mud
and peloids;
forms
exclusively in
marine
environments
Iron oxide
Various including
Fe
2
O
3
(haematite)
and
H
2
Fe
2
O
4
(H
2
O)
x
(limonite)
Red (haematite)
or yellow-brown
(limonite) or
green
None
Often more
apparent on
weathered surfaces
Crystals,
grains,
cements and
as
replacements
*See note on p. 276 about distinguishing between micrite and sparite.
