Minerals in geology (2)

ROCK AND MINERAL TYPES
• Minerals are chemical compounds, sometimes specified
by crystalline structure as well as by composition, which
are found in rocks (or pulverized rocks, known as sand).
• Rocks consist of one or more Minerals, and fall into three
main types depending on their origin and previous
processing history:
o Igneous rocks are ones which have solidified directly from a
molten state, such as volcanic lava.
o Sedimentary rocks are ones which have been remanufactured from previously existing rocks, usually from
the products of chemical weathering or mechanical erosion,
without melting.
o Metamorphic rocks are ones which result from processing,
by heat and pressure (but not melting), of previously existing
sedimentary or igneous rocks.


COMMON MINERALS IN THE EARTH
•

QUARTZ (Silica)

SiO2

•

CORUNDUM (Alumina) Al2O3

•

HEMATITE

•

CALCITE

•

DOLOMITE

•

GYPSUM

OLIVINE

(Mg,Fe)2SiO4

•

PYROXENE

(Mg,Fe)SiO3

•

AMPHIBOLE
(Ca2Mg5)Si8O22(OH)2

•

FELDSPARS
Albite

Fe2O3
CaCO3
CaMg(CO3)2
CaSO4

• FLUORITE

CaF2

PYRITE

FeS2

•

•

Orthoclase
Anorthite
•

KAOLINITE

NaAlSi3O8
KAlSi3O8
CaAl2Si2O8
Al2Si2O5(OH)4

ROCK AND MINERAL TYPES
•

Examples of Igneous Rocks and their constituent minerals
include:

•

Basalt, Gabbro, Rhyolite, Granite
o Feldspar, Quartz, Amphibole, Pyroxine, Olivine

•

Basalt and Gabbro differ not in composition, but in crystallinity;
likewise Rhyolite and Granite.

•

Basalt and Gabbro differ in relative composition, of the five
major constituents above, from Rhyolite and Granite.

•

Basalt and Rhyolite have small crystals because they are
erupted by volcanoes and cool rapidly from the molten state.

•

Gabbro and Granite have large crystals because they cool
slowly from the molten state, underground.


ROCK AND MINERAL TYPES
• Basalt/Gabbro and Rhyolite/Granite differ in their
proportions of the minerals listed above:
o Basalt and Gabbro consist mostly of Pyroxine and
Olivine. Since these minerals consist largely of
magnesium and iron silicates, these rocks are
sometimes called mafic.
o Rhyolite and Granite consist mostly of Feldspar,
Quartz, and Amphibole. They are, hence, sometimes
called felsic rocks.
o There is a continuous range in composition between
the two extremes, of both composition and crystallinity.





ROCK AND MINERAL TYPES
• Examples of Sedimentary Rocks include Limestone,
Sandstone, and Shale.
o Limestone is mostly Calcite (CaCO3) produced by
chemical weathering of Feldspar and other silicate
minerals. Limestone also is produced from the shells
and skeletons of sea life (e.g. plankton and coral).

o Sandstone and Shale are produced from sand (mostly
quartz) and clay minerals (such as kaolinite), which
result from mechanical and chemical weathering of
igneous rocks.
• Examples of Metamorphic Rocks include Marble (from
Limestone) and Slate (from Shale).





The Rock Cycle