Gem Stone and its Properties

In the Name of Allah
who is the Master of
life and death

Introduction to
Gemology and
Physical Properties
of Gemstone

Introduction to Gemology
• Gemology (gemmology) is the science, art and
profession of identifying and evaluating gemstones. It is
considered a geoscienc and a branch of mineralogy.
• Gemology is the study of gemstones. Some dictionaries
define it as the “scientific study of gemstones,” but it is
almost impossible to remove the scientific element.
There are many categories of gemologists. For the
jeweler it is a key element of their business. They need
to be able to answer their customer’s questions and
identify the gems brought into them.
• Some jewelers are academically trained gemologists and
are qualified to identify and evaluate gems.

Gemstone
• A gem is a natural, mineral or organic
substance, that has substantial beauty,
rarity, and durability .

Natural Gemstone
• Natural means that the material was not
made, or assisted in its making, by human
effort.

Mineral Gemstone
• A mineral can be
defined as a crystalline
solid with a specific
chemical formula, and
a regular three
dimensional
arrangement of atoms.
for example, opal and
natural types of glass.
[Faceted iolite, uncut

emerald crystal]

Organic Gemstone
• An organic gem is one that was made by living things,
present or past. Examples include pearls, coral, jet, ivory,
shell and amber. Such gems consist of the molecules
formed by the organism, although these molecules may
have been altered somewhat due to compression or other
geological or chemical forces.

[Organic gems: coral and freshwater cultured pearl earrings, faceted amber
(enlargement showing fossilized insect within the gem]

Physical Properties of Gemstones
• Properties of Gemstones: There are two sets
of characteristics possessed by every
gemstone, and by which they are studied,
identified and evaluated:

– 1) physical properties
– 2) optical properties.

Physical Properties

• Although there are a dozen or more physical
properties which can be measured, in this
course we will concentrate on just a few. In
particular, our focus will be on those which
are either visible directly, or measurable with
minimal equipment, and those which are
most important as indicators of a gem's
identity, and/or its suitability for particular
uses:

Physical Properties

• 1 Cleavage: In the three dimensional
structure of certain crystals, atoms are
bound more tightly to each other in some
directions and more loosely in others. As a
consequence, when strong forces are
applied, relatively clean breaks may occur in
these "weakest link" directions. These
breaks, which can sometimes be so smooth
as to appear to have been polished, are
called cleavages.

Physical Properties

• Not all gems show cleavage however, for example
tourmalines, sapphires, and garnets do not.

[Apatite: two, imperfect (note that cleaved surfaces are somewhat rounded and irregular);
spodumene: two, perfect (note extremely flat, smooth breaks), fluorite: four, perfect]

Physical Properties

• 2 Fracture: Whereas
cleavages occur only in
some gems, and within
those, only in certain
directions, fractures can,
and do, occur in all
gems, and in any
direction. A fracture is a
break which is not along
a cleavage plane [Turquoise: granular, coral: uneven]

Physical Properties
• 3 Hardness: The tendency to resist scratching in a gem is known as its hardness

Moh’s Scale of Hardness:
Hardness
Mineral Absolute Hardness

1 Talc (Mg3Si4O10(OH)2) 1
2 Gypsum (CaSO4·2H2O) 2
3 Calcite (CaCO3) 9
4 Fluorite (CaF2) 21
5 Apatite (Ca5(PO4)3(OH-,Cl-,F-) 48
6 Orthoclase Feldspar (KAlSi3O8) 72
7 Quartz (SiO2) 100
8 Topaz (Al2SiO4(OH-,F-)2) 200
9 Corundum (Al2O3) 400
10 Diamond (C) 1500

Physical Properties

[Talc, the softest on the Mohs' scale, diamond, the hardest]

Physical Properties
• 4 Toughness: The tendency to resist
breaking and chipping is known as a gem's
toughness.
• This property is controlled primarily by two
factors: the readiness of a material to cleave
in single crystal gems, and the presence or
absence of certain structural characteristics
in aggregate

Physical Properties
• 5 Stability: Stability in a gem is a measure of its
ability to resist changes due to exposure to light,
heat and/or chemicals.

• 6 Dehydration: Heat is a factor that can create
problems with certain gems. In some cases, the
mineral comprising the gem is "hydrated", that is,
it contains water molecules which adhere
chemically with varying degrees of tenacity.

Physical Properties

• 7 Light: Some gems can fade or change
color when exposed to light. An extreme
example of this phenomenon is seen in the
rare mineral pyrargyrite which must be kept
constantly under opaque covers or else light
exposure quickly renders its originally red
color completely black.

Physical Properties

• 8 Specific Gravity: Specific gravity, also known
as relative density, differs widely among
gemstones, and is one of their most important
physical characteristics from the viewpoint of gem
identification. Specific gravity (SG) is the ratio of
the weight of one unit volume of the gem to the
weight of the same unit of water. For example, to
say sapphire (corundum) has SG = 4.0, means
precisely that a cubic inch of sapphire weighs four
times as much as a cubic inch of water

References

• www.google.com

Gem Stone and its Properties

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Gem Stone and its Properties (20)

Recently uploaded (20)

Gem Stone and its Properties