Technical University of Mombasa
DCE 2106: GEOTECHNOLOGY I
Lecturer : Jackson Muruda
Email :
Session Six: Mineralogy
ROCK FORMING MINERALS
2.1 Classification and composition
Mineral: This is an inorganic or organic substance that occurs naturally. It
has a chemical composition that leads to formation of an atomic structure
in an organized regular geometric pattern and is crystalline. The crystal
formed has flat surfaces called planes. The planes appear to bind the solid
substance as seen in hand specimens. The crystal structure of a given
mineral is a unique property and all specimens of a given mineral have
identical structures. An aggregate of minerals is known as a rock,
although some rocks are monomineralic when pure.
Minerals were formed by combination of elements that are abundant in
rocks of the earth. Mineral forming processes continues to date and over
2200 minerals have already been identified using optical microscope and
other means. The most abundant elements in the earth crust are as
shown in table 1.
TUM is ISO 9001:2015 Certified
1
, Table 1: Abundant elements in earth crust
Element Composition by weight
(%)
O 45.2
Si 27.2
Al 8.00
Fe 5.80
Ca 5.10
Mg 2.80
Na 2.30
K 1.70
Ti 0.90
All other 1
elements
From the table, over 70% of the composition is represented by oxygen and
silicon. These two elements combine to form (SiO4)-4 complex ion commonly
known as silicate ion. This ion constitutes silicate minerals. Thus, silicates are
the most common rock forming mineral.
Minerals are generally categorized as silicates and non-silicates. Classification
based on chemical composition is universally accepted and is as follows:
Natives: Natives are elements that occur independently, without being chemically
combined with other elements. Such elements include;
Metal group; Gold, Silver Platinun, Nickel, Tin, Zinc, etc.
Semi-metal group; Arsenic, Antimony, Selenium,
Tellurium, etc. Non-metal group; Graphite, Diamond
and Sulphur.
Graphite is prevalent in metamorphic rocks. It is used in making of pencils when mixed
with fine cla It is also used as a lubricant when mixed with oil.
Oxides: Oxides consist of oxygen combined with metallic ions and are divided into two
classes, i.e simple oxides and multiple oxides. A simple oxide has one metal and one
oxygen, while a multiple oxide has two non-equivalent metal atoms. Typical examples
include; Cuprite (Cu2O), Rutile (TiO2) Cassiterite(SnO2), Corundum(Al2O3),
Hematite(Fe2O3), Magnetite(Fe3O4)
Halides: This group of minerals is characterized by halogen anions, i.e. Cl- Br-, F-, I- .
Examples include; Halite (NaCl), Fluorite (CaF2), Cryolite (NaAlF6)
Halite is the most common of the halides hence referred to as common salt. Fluorite
also well know is used in manufacture of opalescent glass and steel as well as in
enamelling cooking utensils.
Carbonates: Carbonates comprise of CO 3
2-
anion and a metal with a valence of 2. They
are group into two groups, i.e. Calcite (CaCO 3) and Dolomite CaMg (CO3)2. Aragonite
has same composition calcite but differ in its optical properties. It is prevalent in
caves, coral reefs and in stalactite caves. Calcite has a cleavage characteristic and is
widespread comprising limestone deposits and marble Sulphides: Sulphides include
TUM is ISO 9001:2015 Certified
2
DCE 2106: GEOTECHNOLOGY I
Lecturer : Jackson Muruda
Email :
Session Six: Mineralogy
ROCK FORMING MINERALS
2.1 Classification and composition
Mineral: This is an inorganic or organic substance that occurs naturally. It
has a chemical composition that leads to formation of an atomic structure
in an organized regular geometric pattern and is crystalline. The crystal
formed has flat surfaces called planes. The planes appear to bind the solid
substance as seen in hand specimens. The crystal structure of a given
mineral is a unique property and all specimens of a given mineral have
identical structures. An aggregate of minerals is known as a rock,
although some rocks are monomineralic when pure.
Minerals were formed by combination of elements that are abundant in
rocks of the earth. Mineral forming processes continues to date and over
2200 minerals have already been identified using optical microscope and
other means. The most abundant elements in the earth crust are as
shown in table 1.
TUM is ISO 9001:2015 Certified
1
, Table 1: Abundant elements in earth crust
Element Composition by weight
(%)
O 45.2
Si 27.2
Al 8.00
Fe 5.80
Ca 5.10
Mg 2.80
Na 2.30
K 1.70
Ti 0.90
All other 1
elements
From the table, over 70% of the composition is represented by oxygen and
silicon. These two elements combine to form (SiO4)-4 complex ion commonly
known as silicate ion. This ion constitutes silicate minerals. Thus, silicates are
the most common rock forming mineral.
Minerals are generally categorized as silicates and non-silicates. Classification
based on chemical composition is universally accepted and is as follows:
Natives: Natives are elements that occur independently, without being chemically
combined with other elements. Such elements include;
Metal group; Gold, Silver Platinun, Nickel, Tin, Zinc, etc.
Semi-metal group; Arsenic, Antimony, Selenium,
Tellurium, etc. Non-metal group; Graphite, Diamond
and Sulphur.
Graphite is prevalent in metamorphic rocks. It is used in making of pencils when mixed
with fine cla It is also used as a lubricant when mixed with oil.
Oxides: Oxides consist of oxygen combined with metallic ions and are divided into two
classes, i.e simple oxides and multiple oxides. A simple oxide has one metal and one
oxygen, while a multiple oxide has two non-equivalent metal atoms. Typical examples
include; Cuprite (Cu2O), Rutile (TiO2) Cassiterite(SnO2), Corundum(Al2O3),
Hematite(Fe2O3), Magnetite(Fe3O4)
Halides: This group of minerals is characterized by halogen anions, i.e. Cl- Br-, F-, I- .
Examples include; Halite (NaCl), Fluorite (CaF2), Cryolite (NaAlF6)
Halite is the most common of the halides hence referred to as common salt. Fluorite
also well know is used in manufacture of opalescent glass and steel as well as in
enamelling cooking utensils.
Carbonates: Carbonates comprise of CO 3
2-
anion and a metal with a valence of 2. They
are group into two groups, i.e. Calcite (CaCO 3) and Dolomite CaMg (CO3)2. Aragonite
has same composition calcite but differ in its optical properties. It is prevalent in
caves, coral reefs and in stalactite caves. Calcite has a cleavage characteristic and is
widespread comprising limestone deposits and marble Sulphides: Sulphides include
TUM is ISO 9001:2015 Certified
2
