PHYSICAL PROPERTIES OF
CRYSTALSMINERALS

CONTENTS
• INTRODUCTION
• PROPERTIES
• IMPORTANT PHYSICAL PROPERTIES
• CONCLUSIONS
• REFRENCE

• A crystal may be defined as a solid polyhedral form of a substance bounded by
smooth geometrical surface called faces
• Crystal word comes greeks word crystallos meaning clear ice
• Crystal may be natural or synthetic . Natural crystals occurring in thousands of
varieties are formed in the earth form natural fluids by their cooling under different
conditions of temperature and pressure.
• Most minerals occur in the form of crystals or crystalline aggregates
• A mineral is a naturally occuring inorganic solid substence that is characterized
with a definite atomic structure
• Deals with most important physical properties of minerals which are studied
megascopically and microscopically for their identification
• Includes explanation of essential features of crystallography with special reference
to minerals

Physical Properties of Minerals

• Minerals are composed of atoms, arranged in a
specific order, with a well defined chemical
composition. It might expect the
microscopic variations will also be
manifested in macroscopic physical and
chemical properties.

• 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).

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

Crystal Forms: Quartz

Feldspar

Intergrown cubic crystals of fluorite

• 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.

• 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.

• 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.

Density and Specific Gravity
• Density :- Defined as the mass divided by the
volume and normally designated by the Greek letter,
row,
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. Note that
water = 1 g cm-3
. S.G. is unitless.
• 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.

• 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).

Mohs’ Hardness Scale

Fingernail Hardness (2.5) Scratches Gypsum (2)

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

Polymorphism and polymorphs
• Substances having the same chemical composition but
different crystal structures.
– e.g. diamond and graphite
• Both minerals are composed of pure carbon, but diamond is
the high pressure polymorph of graphite.
• This gives rise to extremely different physical properties.

Polymorphism
Graphite & CalciteNatural Octahedral Diamond
3 mm
From: http://www.phy.mtu.edu/~jaszczak/diamond.html

Diamond vs. Graphite Crystal Structures
From: http://www.molecules.org/elements.html#diamond
Hardness: 10 Hardness: 1-2

• 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.

Planer Cleavage in Mica

Weak Bonding Yields Planer Cleavage

Amphibole Cleavage ~120/60°

Rhombohedral Cleavage in Calcite

Conchoidal Fracture in Glass

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

Calcite Double Refraction

CONCLUSIONS
• Mineral have different physical properties due to
different internal atomic arrangement and are
impurites
• Based on the physical properties and minerals
classified in to different groups

REFERENCE
• Crystal chemistry (2001) JAK
Tareen TRN Kutty {ISBN 8173712972}
• Basic course in crystallograpy [2001]
JAK Tareen TRN Kutty
• WWW.googal.com

THANK YOU