Minerals, origin, occurrence and associations
Rock forming minerals
Classification, Description and Uses
References.
The following books are also useful compilations of mineral data and descrip
tions.
W.A. Deer, R.A. Howie and J. Zussman (1962, 1974, 1980) Rock Forming
Minerals (Seven Volumes) Longmans, London.
R.W.G. Wyckoff (1964) Crystal Structures. Wiley (New York) (Eight Volumes)
(Vols 1, 2, 3 and 4 contain mineral structures).
T. Zoltai and J. M. Stout (1985) Mineralogy: Concepts and Principles.
Burgess (Minneapolis).
C. Klein and C.S. Hurlbut, Jr. (1993) Manual of Mineralogy (After J.D. Dana,
21st edition). Wiley, (New York
L.G. Berry, B. Mason, and R.V. Dietrich (1983) Mineralogy (Second Edition)
Freeman (San Francisco).
W.H. Balckburn and W.H. Dennen (1988) Principles of Mineralogy .
W.C. Brown, K. Frye (1974) Modern Mineralogy. Prentice-Hall.
Deer, Howie, Zussman (1992) An Introduction to the Rock Forming Minerals
(Second Edition) London Longmans ISBN 0-582-30094-0. 696pp.
Mineralogy
 It is the study of the chemistry, physics
and crystal structure of natural, solid,
crystalline materials known as mineral
i.e. is the study of minerals. It also
includes the study of origin, processes
of mineral formation, their geographical
distribution, classification, as well as
utilization.
Importance of Mineralogy
•
•
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
Minerals are the building blocks of the planet. The
study of the earth materials depends on an
understanding of minerals making up the rocks and
sediments
Mineral resources: Ore minerals are the source of
valuable metals (e.g. Cu, Au) and provide energy
resources like uranium. Certain forms of minerals,
gems, delight the eye as jewelry.
Industrial / agro minerals serve as the raw materials
for manufacturing chemicals, dimension stones,
aggregates (metals) for road and concrete , etc.
Soil formation processes
Unfortunately, not all minerals are beneficial; some
pose environmental hazards (geological hazards)
DEFINITION
 A mineral is a
naturally occurring
homogeneous solid
with a definite
chemical
composition and
ordered atomic
arrangement formed
usually by inorganic
processes.
Explanation of Definition
1 Naturally Occurring
 Minerals are not
synthetic (made in a
laboratory)
 Synthetic
equivalents of
minerals have the
qualifier “syn”after
their names
Explanation of Definition Cont.
2 Homogenous
 Minerals cannot be
broken down into
smaller chemical
parts
 A mineral is
considered a single
“phase” in a
thermodynamic
sense
Explanation of Definition Cont.
3 Solid
 Minerals are not
gases or liquids
 The exception is
liquid mercury
(Hg)
Explanation of Definition Cont.
4 Definite chemical composition
 Minerals are made up of elements which are
present as atoms or ions or radicals
Examples:
silicates:
Si4++ O2- → SiO44carbonates: C4+ + O2- → CO32phosphates: P5+ + O2- → PO43Carbon:
C
Explanation of Definition Cont.
5 Highly-ordered atomic arrangement
 Minerals are formed
by a regularlyarranged internal
framework of atoms
Explanation of Definition Cont.
6 Inorganic
 Minerals are not
organic
compounds (i.e.
composed solely
of C,H,N & O) and
are not biological
in origin
Mineraloid
 Natural materials which resemble minerals in
all ways except for one of the 6 criteria
e.g. volcanic glass –amorphous (only shortrange order)
e.g. Metamict minerals: minerals which have
lost their internal order (destroyed) due to
self-inflicted radiation damage (radioactive
decay of some elements) e.g. Uranium
Crystal and Crystal structure
 Minerals, possess an
ordered internal
arrangement which make
them have regular
geometric forms with
smooth plane surfaces.
This ordered unit form is
known as a crystal.
 Definition:
Crystal is a homogeneous
piece of a mineral bounded
by flat surfaces that formed
naturally as the mineral
grew and has a threedimensional internal orderstructure or lattice
Unit Crystal Cell
 consists of molecules
(e.g. H2O), anionic
groups (e.g. SiO44-, PO43), ions (e.g. Ca2+, Fe2+),
atoms (e.g. Cu, Na) or a
combination of anionic
groups, ions and/or
atoms. The threedimensional internal
order of a crystal is a
repetition of identical
unit crystal cells. This
forms the basis on
which symmetry,
cleavage and other
mineral properties can
be explained.
TYPES OF CRYSTALS
Chemical Formula
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Calcite
CaCO3
Dolomite CaMg(CO3)2
Kyanite
Al2SiO5
Orthoclase KAlSi3O8
Olivine
(MgFe)2 SiO4
Apatite
Ca5(PO4)3(F,Cl,OH)
 Each mineral has a
unique arrangement
and the number of
elements contained in
its crystal structure.
 All minerals have a
chemical formula,
which is an analysis of
the types and amounts
of elements present in
a mineral.
Naming of Minerals
 Minerals are mostly given a name that reflects their
major chemical component (oxides, sulphides,
silicates, carbonates, phosphates etc. Also serves
as the basis for their classification
 Minerals may be given names on the basis of some
physical property or chemical aspect, or they
may be named after a locality, public figure, a
mineralogist etc.
 Examples
 Albite (NaAlSi3O8) form Latin albus (white) due to
its colour.
Naming of Minerals Cont.
 Chromite (FeCr2O4) because of the presence of a
large amount of chromium in the mineral.
 Magnetite (Fe3O4) because of its magnetic
properties.
 Silimanite (Al2SiO5) after Professor Benjamin
Siliman of Yale University (179-1864).
 Franklinite (ZuFe2O4) after a locality Franklin, New
jersey where it occurs as the dominant zinc mineral.
 Rhodonite (MnSiO3) from Greek rhodon (a rose)
due to its characteristically pink colour.
Mineral Formation
 The origin of chemical elements:
Cooling of gaseous elements precipitated first
heavy elements in a form of solid particles dust
according to “Big Bang” theory.
 Formation Processes:
1 Precipitation
2 Sublimation
3 Crystallization
4 Solid - Solid reactions (Recrystallization)
Mineral Formation Cont.
 Precipitation (settling or fall out) from a fluid like H2O.
Within the Earth: by hydrothermal processes, diagenesis,
and metamorphism,
At or near the Earth's surface: by evaporation,
weathering, or biological activity.
 Sublimation from a vapour. This process is somewhat
rarer, but can take place at a volcanic vent, or deep in
space where the pressure is near vacuum.
 Crystallization from a liquid. This takes place during
crystallization of molten rock (magma) either below or at
the Earth's surface.
 Solid - Solid reactions. This process involves minerals
reacting with other minerals in the solid state to produce
one or more new minerals. Such processes take place
during
metamorphism and diagenesis due to
changing temperature and pressure conditions.
Environments
 The environments of mineral formation geologically
are highly varied; within the Earth's crust, different
temperatures and depths result in varied minerals and
on the Earth’s Surface, low temperature lead to
precipitation from saline brine (slightly salty water).
 Based on energy sources environment is groups as:
1 Endogenetic (hypogene)- deep-seated
processes in the interior of the earth.
2 Exogenetic (hypergene)- surface processes (at
or near the earth’s surface as well as in the
atmosphere and hydrosphere).
Mode of Occurrence
 Magmatic- crystallization from a magma or lava
 Pegmatitic – final stage crystallization of magma
 Puematolitic - sublimation from volcanic gases
 Hydrothermal – deposition from hot water and steam
 Metamorphic and Metasomatic – recrystallization of
existing minerals
 Evaporites - sun evaporates water and leaves salt
 Crystallization during diagenesis of sediments
 Formation by oxidation and weathering
In geologic environments where mineral formation
is taking place, the kinds of minerals that form
depend on various factors such as:
(a) Temperature
(b) Pressure
(c) The chemical activity of the water present
(d) The mobility and relative abundance of
chemical element
 The mineral formed is defined by two fundamental
properties:
crystal structure – the geometric arrangement of
the ions (atoms) composing the minerals.
chemical composition- the proportions of
different chemical elements contained.
.
Polymorphism
 The ability of a specific
Graphite
Crystal
Structure
Diamond
Crystal
Structure
mineral to crystallize
with more than one
structure is known as
polymorphism. The
various structures of
such minerals are known
as polymorphic forms or
polymorphs. Examples
are Diamond and
Graphite, Calcite and
Aragonite,
Pseudomorphism
 If a crystal of a mineral is altered so that the
internal structure or chemical composition is
changed but the external form is preserved it
is called a pseudomorph. Thus
pseudomorphs are formed as a result of slow
replacement of a crystal substance by
another substance without any change in the
external form and occasionally also in the
internal structure of the original crystal.
Example Goethite having cubic shape after
Pyrite.
Physical Properties
 The elemental composition and crystal structure
of mineral are not readily visible, therefore the
field identification and description of mineral
species is done on the basis of its physical
properties (external aspects). However, physical
properties are governed by the chemical
composition and the crystal structure of the
mineral.
 Minerals physical properties can be determined
by inspection with a hand lens or by relatively
simple tests on hand specimens
Physical Properties Cont.
 The physical properties of minerals include :
Colour
Streak
Luster
Density (Specific Gravity)
Hardness
Cleavage
Fracture
Tenacity
Crystal habit
Crystal Form, etc.
Streak
 It refers to the colour
of a powder produced
by pulverizing the
mineral. It is
obtained by scraping
or rubbing the
mineral against an
unglazed ceramic
plate (porcelain)
Hardness
 It is a measure of the relative ability of a mineral to
resist scratching (breaking of lattice structure). The
stronger the binding force between the atoms, the
harder the mineral.
 A series of 10 common minerals were chosen as scale (F.
Mohs) by comparison with which the relative hardness
of any mineral can be told.
Hardness Cont.
 Moh Scale of Hardness
3
1
6
4
5
9
10
2
7
8
Talc – 1
Gypsum – 2
Calcite – 3
Flourite – 4
Apatite – 5
Orthoclase – 6
Quartz – 7
Topaz – 8
Corundum – 9
Diamond - 10
Crystal Form
 Crystal form refers to the
general outward appearance
i.e. the geometry of a euhedral
crystal, one with natural
crystal faces that grew
unimpeded.
 A general form is a form in a
particular crystal class that
contains faces that intersect
all crystallographic axes at
different lengths. All other
forms that may be present are
called special forms.
Mineral Classification
 Reasons for this classification are:
1. Minerals having the same anion or anionic group
(oxides, silicates, sulphides halides etc.) dominant in
their composition have unmistakable family
resemblances, than minerals containing the same
dominant cation.
2. Minerals related by dominance of the same anion
tend to occur together or in the same or similar
geologic environment.
3. The scheme agrees well with the chemical practice
in the naming and classification of inorganic
compounds.
Mineral Classification Cont.
 By the character of bonding between atoms the
following types of chemical compounds in minerals can
be distinguished:
1. Free atoms elements. These are minerals that occur
in nature in the native state.
2. Compounds of cations with simple anions (sulphides,
halides and oxides).
3. Compounds of cations with complex anions
Mineral Classification Cont.
Mineralogical
Group
Descript./Examples
Oxides
Oxygen combined with
one or more metals e.g.
Hematite (Fe2O3),
Magnetite (Fe3O4) etc
Hydroxides
Similar to oxides, but
Hydrogen takes the place of
a metal
Halides
Electronegative halogen
ions dominate (Cl-, Br-, F-,
I-). NaCl (salt)
Carbonates
Contains carbonate
radical (CO3) e.g. Calcite
(CaCO3), Dolomite
(CaMg(CO3)2) etc
Nitrates
Contains nitrate
radical (NO3) e.g. Soda
Niter NaNO3
Non-Silicates
Native Elements
Sulphides &
other “ides”
Native metals: gold,
silver, copper, platinum,
iron, arsenic, bismuth
Native
elements: sulphur,
diamond and graphite
(carbon)
Elements complexed
with sulphur (sulphides)
e.g. Pyrite (FeS2)
Others: tellurides,
bismuthides,
antimonides, arsenides,
selenides,
Mineral Classification Cont.
Borates
Contains borate
radical (BO3) e.g. Kernite
{Na2B4O6(OH)2.3H2O)}
Sulphates
Contains sulphate
radical (SO4) e.g. Gypsum
(CaSO4)
Chromates
Phosphates
Contains phosphate
radical (PO4) e.g.
Triphyllite
{Li(Fe,Mn)PO4}, Apatite
{Ca5(PO4)F or Cl}
Vanadates
Contains vanadate
radical (VO4)
Contains chromate
radical (CrO4)
Molybdates
Contains molybdate
radical (MoO4)
Tungstates
Contains tungstate
radical (WO4) e.g. Scheelite
(CaWO4), Wolframite
{(Fe,Mn)WO4}
Arsenates
Contains arsenate
radical (AsO4)
Silicates
Silicates
Built on SiO4 tetrahedra or
derivative. SiO2 (quartz)
Ortho silicates e.g. Olivine,
Ring silicates e.g. Beryl etc.
Chain silicates Amphiboles, Pyroxenes
Sheet silicates e.g. Mica's,
Framework silicates e.g.
Feldspars, Quartz etc
Megascopic Mineral Identification
 Determining the name of a mineral involves testing of
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the physical properties of an unknown mineral for
identification purposes. The observer needs to
systematically note as many properties as possible for
the unknown mineral before consulting the mineral
tables. Below are the key properties to note:
Colour
Luster: Three main types are metallic, submetallic
and nonmetallic
Streak Colour
Cleavage
Cont.
•Fracture
•Crystal Habit
•Hardness
•Specific gravity
•Magnetism
•Optical Properties:
•Fluorescence
•Effervescence
•Luminescence
Composition of the Crust
Element
O
Si
Al
Fe
Ca
Na
K
Wt%
46.60
27.72
8.13
5.00
3.63
2.83
2.59
Atomic%
62.55
21.22
6.47
1.92
1.94
2.34
1.42
Mg
Total
2.09
98.59
1.84
100.00
Volume%
~94
~6
100.00
Composition of the Crust Cont.
 Note that eight (8) elements make up over 98% of the
Earth's crust and that oxygen is the most abundant
element. This becomes even more evident if the elements are
determined on an atomic basis, where we can see that about
63 out of every 100 atoms in the crust are oxygen. On a
volume basis, oxygen makes up about 94% of the crust
because oxygen is a large anion, and the other elements
occur as small cations coordinated by the oxygen anions.
Because of the average composition of the crust, the most
common minerals found in the crust are silicates and
oxides. Of the silicates, the alumina-silicates, like the
feldspars and clay minerals are the most common.
Rock-forming Minerals
 Oxygen and silicon are the most abundant
elements (make up about 74% of the
earth's crust), thus the silicate minerals
are the most common and the largest
group and of greater importance than any
other rock-forming minerals.
 Almost all the igneous rock-forming
minerals are silicates and they therefore
constitute over 90% of the earth’s crust.
Rock-forming Minerals Cont.
 The Si4+ cation is
always surrounded by 4
oxygens in the form of
a tetrahedron structure
such that there is a
residual -4 charge. It is
this SiO4-4 tetrahedron
that forms the basis the
basic (building block)
of all of the silicate
minerals.
Rock-forming Minerals Cont.
 When these SiO4-4 tetrahedrons are linked together,
only corner oxygens will be shared with other SiO4-4
groups. Several possibilities i.e. polymerizations of
the silica (SiO4) tetrahedral exist and give rise to
the different silicate groups as:

Nesosilicates, Sorosilicates,

Cyclosilicates, Inosilicates,

Phyllosilicates and Tectosilicates.
Nesosilicates (Ortho or Island Silicates)
 The SiO4-4 tetrahedra
are isolated and bound
to each other only by
ionic bonds from
interstitial cations.
Their structure depend
chiefly on the size and
charge of the
interstitial cations.
Olivine is a good
example: (Mg,Fe)2SiO4.
Sorosilicates (Double Island Silicates)
 If one of the corner
oxygens is shared
with another
tetrahedron, this
gives rise to the
sorosilicate group.
Referred to as double
island group because
there are two linked
tetrahedrons isolated
from all other
tetrahedrons
Cyclosilicates (Ring Silicates)
 If two of the oxygens
are shared and the
structure is
arranged in a ring
we get the basic
structural unit of
the cyclosilcates or
ring silicates.
Inosilicates (Single Chain Silicates)
 If two of the oxygens
are shared in a way to
make long single
chains of linked SiO4
tetrahedra, we get the
single chain silicates or
inosilicates.
 This group is the basis
for the pyroxene group
of minerals.
Phyllosilicates (Sheet Silicates)
 If three of the oxygens
from each tetrahedral
group are shared such that
an infinite sheet of SiO4
tetrahedra are shared we
get the basis for the
phyllosilicates or sheet
silicates. The basic
structural group is Si2O52-.
The micas, clay minerals,
chlorite, talc, and
serpentine minerals are all
based on this structure.
Inosilicates (Double Chain Silicates)
 If two chains are
linked together so
that each tetrahedral
group shares three of
its oxygens, we can
from double chains,
with the basic
structural group
being Si4O116-. The
amphibole group of
minerals are double
chain silicates
Tectosilicates (Framework Silicates)
 If all of the corner
oxygens are shared with
another SiO4
tetrahedron, then a
framework structure
develops. The basic
structural group then
becomes SiO2. The
minerals quartz,
cristobalite, and
tridymite all are based
on this structure.
General Chemical Formula of the Silicates
 XmYn(ZpOq)Wr,
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X = cations with large ionic radii and small valence numbers
(1 or 2) like K+, Rb+, Ba2+, Na+, and Ca2+ forming a
coordination (C.N.) of 6, 8 or 12 with O
Y = cations with medium size ionic radii and 2 - 4 valence
numbers Al3+, Mg2+, Fe2+, Fe3+, Mn2+, and Ti4+ forming a C.N.
of 6 with O
Z = cations with small ionic radii and large valence
numbers (3 or 4) Si4+ and Al3+, forming a
C.N. of 4 with O
w = usually is OH-1, F-1 or Cl-1 or equivalent
p, q, m, n, r are subscript numbers used to maintain
electroneutrality, where m, n, and r depend on the ratio of p
to q (p:q) which defines the subclass of the silicates.
Aluminosilicates (Al2SiO5) Minerals
Inosilicates (Pyroxenes)
Feldspars
Accessory Minerals
 An accessory mineral is a mineral comprising less than
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
10% (<10%) 0f a rock which makes it insignificant to
classification as compared to essential mineral.
Though there are a good number of them, few will be
considered here. They include:
Zircon (ZrSiO4)
Sphene
Apatite
Staurolite
Mineral Associations
 Minerals will often form in specific environments and
be associated with specific minerals. Sometimes a
mineral is only associated with a certain suite of
minerals. Hence an assemblage of minerals is
invariably diagnostic of the conditions under which
particular rocks formed than the individual mineral.
 An important aid in mineral identification is the
knowledge of characteristic and widespread mineral
associations, which helps by the presence of some
easily recognizable minerals first to presuppose and
then identify other unknown minerals characteristic of
a given association.
Mineral Associations Cont.
 Mineral associations formed in the interior of the
crust (endogenic genesis) differ greatly from
those originated at the crust surface (exogenic
genesis).
 Among the endogenic mineral associations one can
distinguish magmatic, pegmatic,
pueumatolytic and hydrothermal ones.
 Mineral associations of exogenic origin are formed
by chemogenic, organic and mechanical
processes.
Typical mineral assemblages of plutonic rocks
Uses of Minerals
 Minerals are useful in many industries in the past and




today.
Minerals that are used for gems are usually hard.
Artists use certain minerals to carve because of their
softness. Talc, serpentine, jade, and malachite are soft
enough to carve and produce beautiful smooth figures.
The colours of some of the minerals also make them
excellent choices for ornamental uses.
Silicon, used in the computer industry is obtained from
quartz which is composed of silicon and oxygen. There are
many other minerals that are useful to our society; roads we
ride or drive on and the buildings we live learn and work in
all contain minerals from iron, tin, nickel, tin, uranium etc.
EXAMPLES OF MINERALS
EXAMPLES OF MINERALS
GOLD