This document discusses the physical properties that are used to identify minerals, both in the laboratory and field. It describes several key diagnostic properties including: crystal shape and habit, color, diaphaneity, luster, streak, hardness, density, fracture and cleavage, and luminescence. Each property is defined and examples are provided to illustrate how they can be used to distinguish between different minerals. Identifying minerals based on physical characteristics allows geologists to study and classify mineral specimens.

3. The properties of minerals
derive from their composition
and crystal structure, so we
can identify minerals, both in
the laboratory and in the
field, on the basis of physical
properties.

4.  Crystal Shape
 Color
 Diaphaneity
 Luster
 Streak
 Hardness
 Density & Specific Gravity
 Fracture, Cleavage and Parting
 Luminescence

5.  For well-developed
crystals, crystal
form & habit are
excellent diagnostic
properties. It refers
to the overall shape
of a crystal or
aggregate of
crystals. A single
crystals habit is
controlled by the
forms that are
present, the way the
forms combine, the
relative sizes of
crystals and other
features.
• A 2D example showing
how unit cells stack up in
different ways to produce
crystals of different shapes.

6.  The most useful terms describing habit
are self-explanatory. Common ones used
to describe the habit of a single crystal
include :
1.Equant(equidimensional)
•Pyrite Espagne showing Equant
Crystal Shape
2. Acicular (Needle
like)
•Millerite showing Acicular
Crystal Shape

7. 3.Tabular
4.Bladed
•Amphthitalite showing
Tabular Crystal Shape
•Kyanite showing Bladed
Crystal Shape
5.Botryoidal
•Brownish-Red Hematite
showing Botryoidal Crystal
Shape
6.Prismatic
• Calcite showing Prismatic
Crystal Shape

8.  Color is often used for
quick identification of
minerals. In some cases it
can be diagnostic, but in
many it is ambiguous or
even misleading. It is
ambiguous because many
things can give color to a
mineral. Structural
defects in minerals may
also give them color.
Other cases of coloration
may include oxidation or
reduction of certain
elements and presence of
minute inclusions of other
•Multi-colored (Watermelon
colored) Tourmaline

9.  Diaphaneity refers to a mineral’s
ability to transmit light. Some
minerals are transparent. When they
are thick some distortions may occur,
but light passes relatively freely
through them. Minerals that do not
transmit light are called translucent.
Third type of miuneral called Opaque
mineral does not transmit light unless
the mineral is exceptionally thin. Most
opaque minerals have metallic lustre
which sets them apart.

10.  Luster refers to general
appearance or sheen of
mineral. It refers to a way in
which mineral reflects light.
The most common types of
identifications on bases of
luster are classified into
Metallic and Non-Metallic.
Minerals that have shiny
appearance of polished metals
are called metallic luster.
Non-metallic minerals are
• Black-Botryoidal Hematite
showing Metallic Luster

11.  Most common Non-Metallic Luster
includes :(1) Vitreous Luster
(Glassy Appearance)
• Quartz
(2) Resinous Luster
( Resin Appearance)
• Amber

12. (3) Greasy Luster
(Play of Colors)
(4)Silky Luster
(composed of fine fibres)
•Diamond •Asbestos

13. (5) Adamantine Luster
(Bright,shiny)
(6) Pearly Luster
(Pearl like)
•Diamond •Muscovite
(7) Dull
• Niter

14.  The Streak of a mineral is the color it has
when it is finely powdered. Streak in some
cases is a key diagnostic property. It is not
useful property to identify silicates but is
especially useful for distinguishing oxide and
sulfide minerals. It is more reliable than
mineral color & easy to determine. Usual
method to determine streak is to rub the
mineral on the streak plate of hardness 6 or
7. Minerals with hardness above than this
cannot be determined because the hardness
of streak plate is 7. Few minerals have
different color in appearance but have
different streak color like calcite comes in
different color but it’s streak is always
white. Pyrite is yellow but has dark colored

15.  Hardness is one of the better properties of
minerals to use for identifying a mineral. It
is a measure of the mineral’s resistance to
scratching. Mohs Scale, a set of 10
minerals whose hardness is known is used to
rub against the given mineral to know it’s
hardness.

16.  Specific Gravity is measured in relation
to a mineral having Average Specific
Gravity (like Plagioclase). Mineral which is
lighter than the mineral in relation will
have lower specific gravity and the
mineral which is heavier in comparison to
the mineral in relation have higher
specific gravity.
For Example:Borax, sulfur,graphite have
Low G
Azurite, Biotite have
average G

17.  Minerals tend to break along lines or
smooth surfaces when hit sharply.
Different minerals break in different
types of cleavage. Cleavage is defined
using two sets of criteria. The first
criteria describes how easily cleavage is
obtained, described as follows :
• Perfect – Obtained easily, planes
easily distinguishable.
•Good – Cleavage produces with some
difficulty but has obvious cleavage
planes.
•Imperfect – Obtained by difficulty and
some planes are difficult to distinguish.

18.  The second set of criteria is the direction
of the cleavage surfaces. The names
corresponds to the shape formed by
cleavage surfaces (cubic, basal,etc.)
Defined specifically by angles of cleavage
lines as explained :

19.  Fracture describes the quality of the
cleavage surface. Most minerals display
following types of fractures :
Even Fracture
•Chalcopyrite
Uneven Fracture
• Sphalerite

20. Hackly Fracture Splintery Fracture
• Elpidite• Copper

21. Fibrous Fracture Conchoidal Fracture
•Chrysotile •Obsidian

22.  Some mineral emit light when they are
activated by an energy form other than
visible light. Such an effect is called
luminescence. Following are types of
luminescence :
Fluorescence Phosphorescence
Thermoluminescence
Willemite
showing
Fluoroscence
Calcite showing
Phosphorescence
Calcite showing
Thermoluminescence

23. BY-AMAN GUPTA,B.Sc(H)GEOLOGY 1st YEAR