Minerology

Syllabus
• Introduction of Minerals and Crystals,
Mode of Formation of Minerals,
Common Rock forming Minerals and
their abundance, Different method of
study of minerals, Significance of
different physical properties in mineral
Identification, diagnostic Physical
Properties.

What is a Mineral?
• Definition: a 1homogeneous,
2naturally-occurring, 3solid, and 4
generally inorganic substance with
a 5definable chemical composition
and an 6orderly internal
arrangement of atoms
• Does not include “minerals” in the
nutritional sense

1- Homogeneous
 Definition: Something that is the same through and
through Cannot be broken into simpler components
2- Naturally Occurring
 Minerals are the result of natural geological processes
 Man-made minerals are called synthetic minerals (e.g.
industrial diamonds)
3- Solid
 Minerals must be able to maintain a set shape nearly
indefinitely
 liquids are not minerals

4- Definable Chemical Composition
 A mineral can be described by a chemical formula
 Quartz: SiO2
 Biotite: K(Mg, Fe)3 (AlSi3O10)(OH)2
 Diamond: C
5- Orderly Arrangement of Atoms
• Minerals have a fixed atomic pattern that repeats itself over a
large region relative to the size of atoms
– Crystal solid, or crystal lattice: The organized structure of a
mineral
– A glass is not a mineral; no organized structure
6- Generally Inorganic
• Organic: A substance composed of C bonded to H, with varying
amounts of O, N and other elements. C, alone, is not organic!
• Only a few organic substances are considered minerals, all other
minerals are inorganic

Mineralogy
A mineral is a naturally occurring substance that is
solid and stable at room temperature, representable
by a chemical formula, and has an ordered atomic
structure. It is different from a rock, which can be
an aggregate of minerals or non-minerals, and does
not have a specific chemical composition. The study
of minerals is called mineralogy.
There are over 4,900 known
mineral species; over 4,660 of
these have been approved by
the (IMA). International
Mineralogical Association

Crystals
• Crystals
• Minerals bounded by smooth (planar) surfaces
(faces) that are arranged in a symmetrical
fashion.
• Planar surfaces or faces are manifestations of
the internal structure of the mineral, which
is a function of the unique arrangement of
atoms in each mineral.

Crystals
• In the 1600s, scientists realized that crystals are:
• Composed of small building blocks (unit cells).
• These blocks are added in a regular way thus
creating the crystal.
• Each „block‟ or „unit cell‟ contains a small
number of atoms.
• Each „block‟ or „unit cell‟ has the same atomic
composition.
• The „block‟ or „unit cell‟ has the same shape and
symmetry (form) as the entire crystal (sort of
intuitive).

Crystals
• Regular geometric solid bounded by smooth
plane surfaces, characterized by ordered
arrangement of atoms.
• Every atom within a crystal contains an
identical environment.
• The atoms can be related to one another by
geometrical operations – symmetry operations.

Organized Crystal Lattice
• Glass: no
organized
molecular
structure
• Minerals:
organized
molecules
• Example: Quartz
– Although
different crystals
may look
different, they
share certain
consistent
characteristics

Identifying Crystal Structures
• Some mineralogists use x-ray diffraction
patterns to identify minerals.

X-ray diffraction: Laue
photographic method

Seeing Into Crystals
 Modern instrumentation allows us to “see”
atoms.
 A beam of electrons passes through material.
 Atoms scatter electrons, which pass between them.
 A shadow on the detector indicates a row of atoms.
 This principle drives the electron microscope.

Crystal
• Occurance of complete and independent
crystals are rare in nature. Good crystals
develop only under favorable conditions such as
• Slow cooling (i.e.. Slow crystallization)
• Free surrounding to facilitate the crystal growth
in different directions.
• Non interference by the adjacent growing
minerals during solidification.
In nature more than 99 % of minerals are
crystalline and only few are amorphous

Crystal
Characteristics of Crystal
• The following are some of the details relating to
crystals and minerals
• Faces: The crystals are bounded by flat
surfaces which are known as faces.
• Edge: the line of intersection formed by three or
more adjacent faces in a crystal are called solid
angles.
• Solid angles: The point of intersection formed
by three or more adjacent faces in a crystal are
called as solid angles.

Crystal
Distortion
• In spite of perfect internal atomic
arrangement, sometimes crystals develop
faces of different sizes and shapes. This
kind of geometrical irregularities in the
shape is called “ Distortion”.
Interfacial Angle
In crystallography, interfacial angle is the
angle formed in between the normal of
adjacent crystal faces.

Distortion & Interfacial Angles

Crystal
• Simple form and combination
• If a crystal is bounded by all similar or
like faces it is called a simple form. If the
crystal is bounded by dissimilar faces it
is called as combination.
• Crystallographic axes
• These are imaginary lines which interact
at the centre of crystal. The growth or
development of the crystal is considered
to take place along the axes.

Crystal
• Crystal Systems
• The six possible crystal systems are
cubic system, tetragonal system,
hexagonal system, orthorhombic
system, monoclinic system and
triclinic system

Mode of formation of minerals
• Basically there are three kinds of formation of
minerals in nature. They are formed from
magma or out of secondary processes or under
metamorphism.
• Most of the minerals are formed directly or
indirectly out of magma during different stages
of its solidification. Important and bulky rock-
forming minerals such as feldspar, quartz,
pyroxenes, amphiboles, micas, are formed these
ways.
• Some precious minerals such as garnet, topaz,
magnetite are also formed from magmatic
sources.

Mode of formation of Minerals
• In nature, some minerals are formed
from secondary processes like
weathering, precipitation and deposition.
Minerals like calcite, dolomite, salts,
coal, are example of this group.
• Another important mode of formation of
minerals is out of metamorphism. These
minerals are formed under the influence
of high temperature and pressure with or
without active involvement of chemically
active solutions.

Common Rock forming Minerals
• Based on their nature and economic importance,
all minerals are grouped into „ rock forming
minerals” (e.g. feldspar, quartz, biotite mica) and
„economic minerals ‟ some economic minerals by
virtue of their physical properties serves as a
source of extraction of valuable metals. based on
this minerals are groups as metallic minerals
(hematite, galena, chromium, etc) and non-
metallic minerals (asbestos, graphite, and
megnasite).

Civil Engineering Importance
of Rock forming minerals
• Undoubtly, among different minerals of
economic minerals by virtue of their utility and
inherit values are very important. However from
civil engineering point of view, rock forming
minerals are very essential because
• The civil engineers need to know the properties
of rocks precisely to enable them to consider
different rocks for any required purpose i.e. as a
foundation rock, as a road metal, as concrete
aggregate, as building stones, as floorings, or
roofing minerals as decorative material.

Civil Engineering Importance
of Rock forming minerals
• Thus properties of rocks such as
strength, durability, and appearance of
rock can be assessed only with
knowledge of the minerals that form
rock. The economic minerals , since they
are scare, do not influence the properties
of rocks and hence irrelevant from civil
engineering point of view.

Different methods of study
of minerals
• According to the definition, every mineral has its
own chemical composition and atomic
structure. This combination of chemical
composition and atomic structure is unique for
every minerals. This in fact facilitates the study
of minerals in different ways. Common methods
of study and identification of minerals are
• (i) Their physical properties
• (ii) Their chemical composition
• (iii) Optical methods
• (iv) X-ray analysis

Study of Physical Properties
• Physical properties of minerals like color,
shine, hardness, density,etc can be
studied with mere observation of small
mineral specimen.
• Since the minerals invariably possess its
own specific chemical composition and
atomic structure every minerals should
possess its own physical properties.

Study of Chemical Composition
• According to the definition, every mineral
is expected to have its own distinctive
chemical composition, which is not to be
found in any other mineral. Therefore, by
chemical analysis, if the composition is
known it should be possible to identify
the minerals

Study of Optical Properties
• In this method of study, the minerals are
ground very fine and fixed over glass
slides. They are studied under
petrological microscope. Different optical
properties are studied under polar
microscope. The properties of minerals
like, color, relief, cleavage, shape and
pleochroism are studied under polarized
light.

Study of Optical Properties
• The principle which makes this method
useful for study and identification of
minerals is that when polarized light
passes through thin sections of minerals
it is influenced in a characteristic way
depending on the chemical composition
and atomic structure of the minerals.

X-ray Analysis
• X-ray analysis makes use of the definite
atomic structure, found in every mineral.
X-ray are similar to light wave but have a
much shorter wavelength, comparable to
the distance between atom in a
crystalline mineral.

X-ray Analysis
• When a beam of x-ray falls on a crystal, it is
diffracted by the layers of atoms within a
crystal, in making an x-ray analysis of the
atomic structure of the crystal, the diffracted x-
rays are allowed to fall on a photographic plate,
and the resulting photograph shows a series of
spots or lines which form more or less
symmetrical pattern. Thus x-ray analysis of
minerals reveal their actual atomic structure,
which is distinctive for each minerals. This
enables the accurate identification of minerals.

Minerals : Physical Properties and Crystal Forms
From: http://webmineral.com/data/Rhodochrosite.shtml

The Physical properties of minerals are used
by Mineralogists to help determine the
identity of a specimen. Some of the tests can
be performed easily in the field, while others
require laboratory equipment. For the
beginning student of geology, there are a
number of simple tests that can be used with
a good degree of accuracy.
The Physical Properties of Minerals

• Color
• Streak
• Luster
• Hardness
• External Crystal Form
• Cleavage

(cont.)
• Fracture
• Specific Gravity
• Special Properties
• Degree of Transparency
• Other Properties
• Chemical Tests

Mineral Identification
• Since we can‟t all have x-ray diffraction machines and electron
microscopes, we identify minerals by visual and chemical
properties called physical properties.
• Types of physical properties that geologists use include:
– Color, Streak, Luster, Hardness, Specific Gravity,
Crystal Habit, and Cleavage
Pyrite
 Properties depend upon…
 Chemical composition.
 Crystal structure.
 Some are diagnostic.
 Minerals have a unique set of
physical properties.

1- Color
• Color may be diagnostic
for a few minerals, but in
general, a given mineral
can have a range of colors.
Various colors of quartz, SiO2
Hematite (Fe2O3) can have various colors, but its
streak is always red-brown
2- Streak
 The color of the pulverized
powder of a mineral.
 More consistent than
color
 Found by scraping a
mineral against a
porcelain plate

Important Physical Properties
• Color - Although an obvious feature, it
is often unreliable to use to determine
the type of mineral.
 Color arises due to electronic transitions,
often of trace constituents, in the visible
range of the EM spectrum. For example,
quartz is found in a variety of colors.
• Color of a mineral may be quite
diagnostic for the trace element and
coordination number of its bonding
environment.

Hope Diamond: 44.5 carats
http://www.nmnh.si.edu/minsci/hope.htm

Color
• Colour : Colour is the first thing someone
notices when they view a mineral. Color is also
one of the big reasons that attract people to
minerals. Generally speaking, color is not a
good property to be used in the identification of
minerals. It is usually the first property to
confuse a novice collector into making an
incorrect identification.
• Minerals having Property of Green, Golden
Yellow, Yellow, White, Red, Blue, Black, Grey,
Purple & Transparent Colour.

• Streak - The color of a mineral in
its powdered form; obtained by
rubbing the mineral against an
unglazed porcelain plate.
• Streak is usually less variable than
color.
• Useful for distinguishing between
minerals with metallic luster.

3- Luster
• The way a mineral‟s
surface scatters light
Metallic luster
4- Hardness
• The measure of a mineral to
resist scratching
• Represents the strength of
bonds in the crystal lattice
– Measured on a qualitative
scale called Mohs
Hardness Scale
Nonmetallic luster
Vitreous
luster
(Nonmetallic)
Adamantine luster
(Nonmetallic)

• Luster - This property describes
the appearance of reflected light
from the mineral's surface.
Nonmetallic minerals are described
using the following terms: vitreous,
pearly, silky, resinous, and earthy.

Luster
Lustre is a description of the way a mineral surface
looks when light reflects off of the surface.

• Hardness - This is the resistance of the
mineral to abrasion or scratching. This
property doesn't vary greatly from sample
to sample of the same mineral, and thus
is highly diagnostic. It also is a direct
reflection of the bonding type and
internal atomic arrangement. A value is
obtained by comparing the mineral to a
standard scale devised by Moh, which is
comprised of 10 minerals ranging in
hardness from talc (softest) to diamond
(hardest).

Hardness
• The hardness of a mineral is a way of
describing how easy or difficult it is to
scratch the mineral. It is used, in
combination with the other physical
properties, to help identify a mineral
specimen

Mohs scale of mineral
hardness
• The Mohs scale of mineral
hardness characterizes the scratch resistance of
various minerals through the ability of a harder
material to scratch a softer material.
• It was created in 1812 by the
German geologist and mineralogist Friedrich
Mohs.

hardness

hardness
• The Mohs scale of mineral hardness is based on the
ability of one natural sample of matter to scratch another
mineral. The samples of matter used by Mohs are all
different minerals. Minerals are pure substances found in
nature. Rocks are made up of one or more minerals. As
the hardest known naturally occurring substance when
the scale was designed, are at the top of the scale. The
hardness of a material is measured against the scale by
finding the hardest material that the given material can
scratch, and/or the softest material that can scratch the
given material.

Mineral Hardness
The Moh's Scale of Hardness:
Talc Gypsum Calcite
Fluorite Apatite Orthoclase Feldspar

Mineral Hardness
The Moh's Scale of Hardness:
Quartz Topaz Corundum
Diamond

Moh’s
Hardness
Scale
• Fingernail = 2.5
• Glass = 5.5
• Streak Plate = 6.5
• Talc =1
• Quartz = 7
• Diamond = 10
This doesn’t mean
that diamonds are
10 times harder
than talc…
that’s why we call this
a qualitative
measure, not
quantitative
measure

5- Specific Gravity
 Specific Gravity: The weight of a substance
divided by the weight of an equal volume of water
6- Crystal Habit
• A description of a mineral‟s
consistent shape
Prismatic
Blade-like or
Elongated
Needle-like or
fibrous

Density and Specific Gravity
• Density - Defined as the mass divided by the
volume and normally designated by the
Greek letter, rho, Mass/ Volume; SI units: kg/m3
or kg m-3, but geologists often use g/cm3 as the unit
of choice.
• Specific Gravity - Ratio of the mass of a
substance to the mass of an equal volume of
water. S.G. is unit-less.
• Examples - quartz (SiO2) has a S.G. of 2.65
while galena (PbS) has a S.G. of 7.5 and gold
(Au) has a S.G. of 19.3.

Specific Gravity
• Specific Gravity : Specific Gravity of a
mineral is a comparison or ratio of the
weight of the mineral to the weight of an
equal amount of water. The weight of the
equal amount of water is found by
finding the difference between the weight
of the mineral in air and the weight of
the mineral in water.

Specific Gravity
• Specific Gravity (G) = mass of subs./mass of
equiv. Vol. H2O at 4ºC
• Silicates ~ 2.5
• Gold ~ 19
• Galena ~ 7.5
• 45
• Specific Gravity is a „way‟ of expressing density.
• Density: weight/unit volume (g/cm3)

• Crystal form or habit - The external
morphology of crystals generally reflect
the internal arrangement of their
constituent atoms. This can be
obscured, however, if the mineral
crystallized in an environment that did
not allow it to grow without significant
interaction with other crystals (even of
the same mineral).

External Crystal Form
• Crystal structure results from the orderly
geometric spatial arrangement of atoms in the
internal structure of a mineral. This crystal
structure is based on regular internal atomic
or ionic arrangement that is often expressed in
the geometric form that the crystal takes. Even
when the mineral grains are too small to see or
are irregularly shaped, the underlying crystal
structure is always periodic and can be
determined by X-ray diffraction.

Crystal Form
 Crystal form is the external expression of the internally ordered arrangement of
atoms.
 During mineral formation, individual crystals develop well-formed crystal faces
that are specific to that mineral.
 The crystal faces for a particular mineral are characterized by a symmetrical
relationship to one another that is manifest in the physical shape of the
mineral‟s crystalline form.
 Crystal forms are commonly classified using six different crystal systems, under
which all minerals are grouped.
1. Isometric (Cubic)
2. Tetragonal
3. Orthorhombic
4. Hexagonal
5. Monoclinic
6. Triclinic
The six major crystal forms:
Axes and Angles
C
BA



Crystal Form, cont.
 Isometric:
Isometric crystals are block shaped with relatively
similar and symmetrical faces. The crystal form has
three axes all at 90° angles and all the same length.
Mineral Example: Pyrite
Tetragonal:
Tetragonal crystals are shaped like four-sided
pyramids or prisms. The crystal form has three
axes that are all perpendicular to one another. Two
axis have the same length, and one is different. The
axes that are the same length lie on a horizontal
plane, with the third axis at a right angle to the
other two. Mineral Example: Zircon
Orthorhombic:
Orthorhombic crystals are shaped like a
rectangular prism with a rectangular base. The
crystal has three axes of different lengths and
intersect at 90° angles. Mineral Example: Topaz
Copyright© Dr. Richard Busch
Isometric: Pyrite
Tetragonal: Zircon
Copyright© Dr. Richard Busch
Axes Length Relationships: A = B = C
Angles:  =  =  = 90
A
C
B
A B
C
Axes Length Relationships: A  B  C
Angles:  =  =  = 90
C
BA
Axes Length Relationships: A  B  C
Angles:  =  =  = 90
Orthorhombic: Topaz
Photo Courtesy USGS77
Table of Contents
C
BA



Crystal Form, cont.
Hexagonal:
Hexagonal crystals have three symmetrical axes that occur
in the same plane and are all the same length. The fourth
axis may be either longer or shorter, and it intersects the
other three axis at 90° angles. The sides intersect at 120 °
angles. Mineral Example: Amethyst
Monoclinic:
Monoclinic crystals are short and stubby with tilted faces.
Each crystal has three axes that are unequal. Two of the
axes lie in the same plane at right angles to each other, the
third axis is inclined. Mineral Example: Gypsum
Triclinic:
Triclinic crystals have three axis which are all different
lengths and all three axis intersect at angles other than 90°.
Mineral Example: Kyanite
Monoclinic: Gypsum
Copyright © Stonetrust ,Inc.
A
B
D
C
A
B
C
A
B
C
Axes length Relationships: A = B = C ≠ D
Angles:  =  = 90 and  =
120
Axes Length Relationships: A ≠ B ≠
C
Angles:  ≠  ≠ 
Axes Length Relationships: A ≠ B ≠ C
Angles:  ≠  =  = 90
Hexagonal: Amethyst
Triclinic: Kyanite
C
BA



Chrysotile
Asbestos
Belongs to the Serpentine mineral family -
hydrated ferromagnesian silicate.

Intergrown cubic crystals of fluorite

Quartz Interfacial Angles
Perfectly
Proportioned
Crystals
Misshapen
Crystals
Steno’s Law (1669): Crystal face internal angles remain constant!

Macroscopic Forms and Microscopic Blocks
Cubes
Rhombs
Macroscopic
Crystal Forms

Unit Cells and Crystal Structure
Cubic unit cell:
smallest repeatable unit

Fracture and Cleavage
• Cleavage: The tendency of a
mineral to break along a plane of
weakness in the crystal lattice.
• Fracture: The mineral breaks in
no consistent manner
– Equal bond strength in all
directions
• Conchoidal Fracture: The
tendency for a mineral to break
along irregular scoop-shaped
fractures that are not related to
weaknesses in the crystal structure
Obsidian, a volcanic glass, and
quartz commonly exhibit conchoidal
fracture, which is why Indians used
them as cutting tools.

• Cleavage - Orientation and number of planes of
weakness within a mineral. Directly reflects the
orientation of weak bonds within the crystal
structure. This feature is also highly diagnostic.
• Fracture - This describes how a mineral breaks if
it is not along well defined planes. In minerals
with low symmetry and highly interconnected
atomic networks, irregular fracture is common.

Weak Bonding Yields Planer
Cleavage

Rhombohedra Cleavage in Calcite

Cleavage
• Tendency to break along planes of weakness.
• Cleavage produces flat, shiny surfaces.
• Described by number of planes and their angles.
• Sometimes mistaken for crystal habit.
– Cleavage is through-going; often forms parallel “steps.”
– Crystal habit is only on external surfaces.
• 1, 2, 3, 4, and 6 cleavage planes possible.

Cleavage
 Examples of
Cleavage:
 1 direction
 2 directions at 90º
 2 directions NOT at
90º
Muscovite Mica
Amphibole
Potassium Feldspar

 Examples of Cleavage:
 3 directions at 90º
 3 directions NOT at 90º
Cleavage
Calcite
Halite

Cleavage
• Cleavage - Cleavage is the tendency of
minerals to break along preferred
directions. Some minerals tend to have
one direction of cleavage.

Fracture
• Fracture - Fracture represents a mineral
break other than along a cleavage or parting
plane. Breaks may occur in any direction
but are usually around some imperfection in
the mineral.

Degree of Transparency
• This is also known as „ diaphaneity‟
depending upon the resistance offered by
the minerals to the passage of light
though them, they may be classified as
transparent ( rock crystal, ice landspar)
Translucent (calcite, agate) and opaque
(galena, ilmenite, pyrite) .

Degree of Transparency
• This character of a mineral depends
on the chemical composition,
impurities present, inclusions,
weathering, and also on thickness.
Rock forming minerals usually
appear opaque, when they are
thick, but they lose this opaque
character if they are made thinner

Special Characteristics
• There are other special characteristics that some minerals exhibit
that allow us to identify them
– Reacts to Acid [Calcite and Dolomite: CaCO3 & Ca(Mg)CO3]
– Magnetic [Magnetite: Fe3O4]
– Salty taste [Halite: NaCl]
– Striations [Plagioclase Feldspar: NaAlSi3O8 - CaAl2Si2O8, Pyrite -
FeS2, Quartz - SiO2]
Striations on Pyrite Calcite reacts with HCl and gives off CO2

Special and Other Properties
• Striations - Commonly found on plagioclase
feldspar. Straight, parallel lines on one or
more of the cleavage planes caused by
mineral twinning.
• Magnetism - Property of a substance such
that it will spontaneous orient itself within a
magnetic field. Magnetite (Fe3O4) has this
property and it can be used to distinguish it
from other non-magnetite iron oxides, such
as hematite (Fe2O3).
• Double Refraction - Seen in calcite
crystals. Light is split or refracted into two
components giving rise to two distinct
images.

Plagioclase
striations
Striations

Minerology

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