Gemstones

1. A Seminar on
Precious Gem Minerals and their
Characters with Reference to the
Indian Occurrences

2. CONTENTS
 Introduction
 Characteristics
 Diamond
 Ruby
 Sapphire
 Emerald
Indian Occurrences
 Diamond
 Ruby
 Sapphire
 Emerald
Conclusions
References

3. •Gemstones are minerals with special beauty and physical
properties that attract attention for possession.
•The main characteristics of a gemstone are its color, rarity
and durability.
•The cut stones are known as gems while the uncut ones are
known as gemstones.
•The gemstones are grouped into:
 Precious gemstones namely diamond, ruby, sapphire
and emerald.
 Semi-precious gemstones: aquamarine, moonstone,
amethyst, etc.

5. Characteristics
Diamond
 It is a natural crystalline form of the chemical
element carbon (C) and the only gemstone made up
of a single element.
 It is the most durable and hardest gemstone, with a
Moh’s scale hardness of 10.
 It crystallizes in the cubic system and the crystals are
mostly octahedral or dodecahedral.
 It possess perfect cleavage and hackly or more rarely
conchoidal fracture.
 It has a varying specific gravity of 3.47 to 3.56
depending upon its chemical purity.

7.  Diamond is isotropic and has a very high refractive
index of 2.41 to 2.43.
 It possess adamantine lustre.
 The color ranges from colorless to yellow, pink, red,
orange, green, blue, brown and black.

8. Ruby
 Ruby is a variety of the mineral corundum whose
chemical composition is Al2O3.
 The red variety of corundum is known as ruby.
The red color is due the presence of chromic
oxide.
 Crystal system of ruby is trigonal.
 The hardness of ruby is 9 which makes it the
hardest gemstone next only to diamond.
 The specific gravity of ruby is 3.94-4.1 and the
refractive index is 1.76-1.77.

9.  Ruby exhibits no true cleavage and fracture maybe uneven or conchoidal.
 The lustre is vitreous with transparent diaphaneity and the streak is white.
 The optical properties of ruby are:
 It is Optically uniaxial.
 Shows Negative Birefringence.
 Pleochroism is very strong showing violet to dark red and paler red with a
touch of yellow.

10. Sapphire
 Sapphire is the blue variety of corundum. The
blue coloration is due to the presence of iron and
titanium.
 The chemical composition is Al2O3. Crystal
system is trigonal.
 The hardness is 9, streak is white and the fracture
is conchoidal.
 There is no cleavage, luster is vitreous and its
specific gravity is 3.94-4.1
 The refractive index is 1.76-1.77.

11.  Optical properties:
 It is Optically uniaxial.
 Shows Negative Birefringence.
 Pleochroism, is stronger than in ruby shows two color clear
blue and greenish-blue.

12. Emerald
 Emerald is a variety of the mineral Beryl and is
green in color. The traces of chromium and
sometimes vanadium gives the green color.
 Its chemical composition is (Be3Al2(SiO3)6) and
belongs to hexagonal crystal system.
 It has a hardness of 7.5 to 8.0, white streak,
vitreous lustre and imperfect cleavage.
 It exhibits opaque to transparent diaphaneity and
has a specific gravity of 2.76.
 The R.I. is 1.57-1.58.

13.  Optical properties:
 Uniaxial
 Negative birefringence
 Pleochroism – two colors pale yellowish green and
bluish green

14. Indian occurrences
 Diamond deposits in India occur in three
geological settings:
 Kimberlite pipes – Wajrakarur in Anantpur
district of A.P.
 Conglomerate beds – Panna, M.P. and
Kurnool district of A.P.
 Alluvial gravels – gravels of Krishna river
basin, A.P.
Other localities are in Uttar Pradesh, Orissa,
Bihar and Maharashtra.

15. RUBY
 A.P., Khammam district – country rocks are
sillimanite corundum rocks-metamorphosed
schists and pegmatites.
 Karnataka (Bangalore , Mysore, Kolar) –
spordiac occurrences at the contact of basic and
ultra basic rocks with the country rocks.
 M.P., Bastar – semi-gem ruby in schist and
gneisses, intruded by plagio-granite and
metabasic dykes.
 T.N., Salem and Dharmapuri – ruby is
occasionally picked along with corundum.

16. SAPPHIRE
 Jammu & Kashmir, Doda – occurs in syenite and
pegmatite, intruding actinolite-tremolite-schists.
 Nearby alluvial placers also worked
intermittently but the mine remains closed since
1973.

17. EMERALD
 Rajasthan, Udaipur – found at the contact of
pegmatites intruding schists, mainly amphibole
schists.

18. Conclusion
 Gemstones are special minerals which are rare and
exhibit exceptional hardness.
 Gemstones are classified as precious and semi-precious.
 The precious gemstones are diamond, ruby, sapphire and
emerald.
 These precious gemstones are very essential not only in
the jewellery industry but also other industries due to
their exceptional hardness and optical properties.
 India boasts of having all these four gemstone deposits in
various geographical and geological settings.

19. Reference
BOOKS:
 Prasad, Umeshwar, 2000. Economic Geology: PP:178-189, Patna,
India.
 Borner, Rudolf, 1962. Minerals, Rocks and Gemstones: PP:220-
223, London, U.K.
WEBSITES:
 http://en.wikipedia.org/wiki/Diamond
 http://en.wikipedia.org/wiki/Ruby
 http://en.wikipedia.org/wiki/Sapphire
 http://en.wikipedia.org/wiki/Emerald

20. Thank you!!!!!