2. OUTLINE
INTRODUCTION
: What are Gems ??
GENERAL CHARACTERISTICS
: At a glance
WHAT MAKES IT SPECIAL?
ABOUT SOME GEMS
: To Mesmerize
FINALLY
: Benefits
REFERENCES
3. INTRODUCTION
What is a GEM ?
Gems are expensive sparkling
mineral stones.
A Gem can be a Natural, or Synthetic
ceramic. There are about 150 of them.
It provides a link between
Crystallography ,Mechanical testing,
solid-state ,physical and inorganic
chemistry ,electrical engineering.
4. GENERAL
CHARACTERISTICS
150 natural compounds used as gems.
Diamonds, emeralds, rubies, and sapphires
sell at highest prices
Followed by amber, aquamarine, jade, opal,
pink topaz, and tourmaline with intermediate
values
Agate, amethyst, and zircon with lower
values
They are inorganic solid .
It possess an orderly internal structure, that is,
its atom must be arranged in a definite pattern.
They have definite chemical composition that
may vary within specified limits.
5. What makes them special and
ATTRACTIVE ??
What makes them different from
normal stone??
Color :
One of the main features.
They are many different reasons for these colors.
It could be because of their composition.
Cr makes emerald GREEN and rubies RED.
Refractive Index :
The higher the value of the refractive index of
a properly cut gem ,within limits, the more light will
return to the eye of the viewer, resulting in its
BRILLIANCE.
Diamond has a particularly high value of n=2.417.
6. Dispersion :
Dispersion causes rays of light to be split into
their colored components that can emerge in slightly
different directions. The dispersion is 0.044 for
diamond, one of the highest values for a natural
gemstone.
Color is related to the wavelength of
light and dispersion experienced by it.
7. Absorption :
The other factor that is particular to
different materials is the optical absorption
.The absorption spectrum can easily
distinguish different gems.
Hematite is gray unless the light passes
through it ,in which case it appears red. (hence
its name). The reason for the red color is that
hematite absorbs blue light.
Some
gemstones
can be
identified by
the spectral
colors they
produce
Ruby colored by chromium Almandine garnet colored by iron
8. Facets:
The faceted gemstone is ideally shaped to
optimize its sparkle, i.e., maximize the amount of
light that is reflected back to the observer. The
object of faceting is to make the most of total
internal reflection.
Pleochroism :
When ‘n’ of a crystal varies with the direction in
which light travels through it, the absorption can be
different in different directions. The crystal then
shows a different color when viewed in different
direction. If there are two distinct directions, the
gem’s crystal structure is dichroic, it can be trichroic
too.
9. This is what makes
them expensive
A Diamond is Forever !!
BeautyBeauty
RarityRarity
TraditionTradition
Perception ofPerception of
permanencepermanence
10. OTHER PROPERTIES
Hardness:
Diamond is so hard ,it is used to cut glass and other
diamonds even. Diamond is the- hardest natural material,
140 times harder than corundum The hardness of a
gemstone is referred to as its Mohr’s hardness. The test
is called Mohr’s hardness test.
Chemical stability:
Gemstones are always thought to be stable ,but some
of them are not so stable. Opal contains a significant
amount of water ; if this water is removed , then the opal
will fracture and degrade. Emeralds are slightly different
in that they usually already contain many fractures that
have been filled with oil or polymer.
Diamond is durable .
11. DIAMONDS AND
ASSUMPTIONS AROUND IT !!
Why diamond??, yes ,its hard ,but its optical
qualities that have made it so popular !!
It can get us good understanding about gems
as it is definitely not unheard of !!!
It doesn’t have the best optical properties.
The refractive index of diamond is 2.42
whereas the refractive index of moissanite and
rutile are 2.69 and 2.65 .
The common assumption is gems are poor
conductors of heat ,but diamond is actually a
much better thermal conductor than Cu.
12. De Beers in Africa is the largest supplier of rough
diamonds in the world. Measured in carats.
14. RUBIES &
SAPPHIRES
It’s mainly Al203.
If the stone is RED ,it is called ruby ;
If it is any other color, it is called sapphire
or fancy sapphire.
There are many ways to produce the color,
Ruby is Cr doped ,while the blue gemstones contain the Fe-Ti complex
Sapphires can be colored using dopants .
Doping with Be is quite new.
The Corundum Group
15. EMERALD
AND
BERYLS
The mineral is generally referred as
BERYL.
It is the principal source of Be.
It occurs in three forms :
Emerald , Precious Beryl , Aquamarine.
The formula Be3Al2Si6O18.(with up to 1H2O);
It has n=1.595. The crystal structure is hexagonal and
is composed of 6-fold rings of SiO4 tetrahedra,
which make up the Si6O18 unit.
16. OPAL
Natural opal are deposited in fissures in rocks or fossilized wood.
They consist of perfect arrays of identical spheres of SiO2.
The spheres have a radius of about 300nm,so arrays of the spheres
look like crystals to incident visible light .Thus the light is diffracted ,
which is why we see different colors when viewing opal from different
directions.
The spheres can be amorphous or partially crystalline.
Not all opal shows these colors since the term
opal refers to any material made up of such SiO2 spheres;
17. OTHER GEMS !!
Quartz crystals are known by different names.
The colorless form is known as rock crystal.
Amethyst is a single-crystal quartz.
The crystals grew naturally by a
hydrothermal process
The purple color can be used by Fe that is in the +4 state due to natural
or artificial irradiation or by Mn.
When heat treated, the stones become yellow-orange-brown and
are known as citrine
18. TOPAZ
It is a silicate with general formula
Al2SiO4(F2OH)3. It is the hardest silicate,
the crystal is unusual .It is orthorhombic
consisting of chains of AO6 octahedra linked
with SiO4 tetrahedra.
It is found in a variety of shades of blue and
the imperial yellow. The stones may be
radioactive after some days of processing.
19. ARE THESE ONLY FOR DECORATIVE
PURPOSE ??
Tourmaline crystal is used to study Double
refraction. And the concept of double refraction is
useful in LCD’s
Piezoelectricity : electricity can be induced in
quartz crystals ,when electric field is applied to
induce dimensional change.
Healing crystals and gemstones are one of the
most beautiful ,mystical ,and profound “energy
medicine”, a tool which have been used since
ages. Like yellow sapphire is beneficial for people
having fever , cough, rheumatism etc. It is
believed to be so !!
