The document discusses precious gem minerals found in India, including their characteristics and locations. It describes the properties of diamond, ruby, sapphire, and emerald, such as crystal structure, hardness, refractive index, and color. Diamond deposits are found in kimberlite pipes, conglomerate beds, and alluvial gravels. Ruby, sapphire, and emerald occurrences are located in various states where the minerals are associated with intrusions of basic and ultra-basic rocks into other rock types. India has commercially significant deposits of all four precious gem minerals.

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!!!!!