This document provides information on various gemstones, including their composition, properties, and sources. It discusses key stones like diamond, which is a crystalline form of carbon; corundum, which forms ruby and sapphire; emerald, a variety of beryl; and quartz, which has many colored varieties used in jewelry. It also covers other gemstones such as tourmaline, olivine, zircon, and tiger's eye. For each it provides details on color, crystal structure, hardness, refractive index, and countries where they are found in nature. The document aims to classify and characterize important gemstones through descriptions of their physical and optical properties.

1. Shaumik Daityari
GLT, 2nd year

2. Gemstone
A gemstone or gem (also called a precious or semi-
precious stone, a fine gem, or jewel) is a piece of
mineral, which, in cut and polished form, is used to
make jewellery or other adornments.
Certain other materials (like amber) which are not
minerals, used to make jewellery, are also called
gemstones.

3. Classification
Traditional classification in the West: Precious
(diamond, ruby, sapphire and emerald) and Semi-
precious
Chemical Composition: Carbon (Diamond),
Aluminium Oxide (Ruby)
Crystal System: Cubic (Diamond), Hexagonal
(Tourmaline)
Groups and Varieties
Refractive index, dispersion, specific gravity,
hardness, cleavage, fracture, luster, pleochlroism,
birefringence, inclusions
In terms of their “water”: first second and third water

4. Cutting and Polishing
A citrine preform and the finished faceted stone.
Raw
Gemstones

5. Cutting and Polishing
The process of cutting and polishing gems is
called gemcutting or lapidary.
Gemstone material that has not been extensively
cut and polished is referred to generally as
rough. Rough material that has been lightly
hammered to knock off brittle, fractured material
is said to have been cobbed.
All gems are cut and polished by progressive
abrasion using finer and finer grits of harder
substances.
Diamond and Silicon Carbide used as abrasives.

6. Treatment
Gemstones are often treated to
enhance the colour or clarity of the
stone. Depending on the type and
extent of treatment, they can affect
the value of the stone. Some
treatments are used widely
because the resulting gem is
stable, while others are not
accepted most commonly because
the gem colour is unstable and
may revert to the original tone.

7. Diamond
Diamond (from the ancient Greek –
adámas "unbreakable") is an allotrope of
carbon, where the carbon atoms are
arranged in a variation of the face-
centered cubic crystal structure called a
diamond lattice.
Excellent optical and mechanical
properties, combined with efficient
marketing, make diamond the most
popular gemstone.
Most natural diamonds are formed at high-
pressure high-temperature conditions
existing at depths of 140 to 190 km (87 to
120 mi) in the Earth mantle. Russia, Bostwana, Australia and Congo
Found in U.S, South Africa,

8. Diamond
Color: Typically yellow, brown or gray to colorless.
Crystal habit: Octahedral Crystal system: Cubic
Cleavage: 111 (perfect in four directions) Fracture:
Conchoidal
Hardness: 10 Luster: AdamantineStreak:
Colorless
Diaphaneity: Transparent Specific gravity: 3.52
Optical properties: Isotropic Refractive index:
2.418

9. Diamond Thin Section (PP)
Colour: Colourless
Cleavage: Perfectly
Octahedral
Relief: Extremely High

10. Diamonds can be
identified by their high
thermal conductivity.
Their high refractive
index is also indicative.
Also have fairly high
dispersion.
Diamonds can scratch
other diamonds, but Most gemologists still rely upon
this can result in skilled use of a loupe
damage to one or both (magnifying glass) to identify
stones. So hardness diamonds 'by eye'.
tests rarely used.

11. Corundum
Corundum is a crystalline form of
aluminium oxide with traces of iron,
titanium and chromium.
The name "corundum" is derived
from the Tamil word "kuruntam"
meaning “ruby”.
Mostly found in Greece and US

12. Corundum
Color: Colorless, gray, brown; pink to pigeon-blood
red
Crystal habit: Rhombohedral crystals, massive or
granular
Crystal system: Trigonal (Hexagonal
Scalenohedral)
Cleavage: None, Rectangular Parting Hardness:
9
Luster: AdamantineTransparency: Translucent
Specific Gravity: 3.9 - 4.1 Streak: White

13. Corundum: Optical
Properties
Colour: Colourless, pale pink, green, blue or yellow
Relief: Very High
Pleochlroism: Yes
Uniaxial (negative)
Extinction: Parallel
Weakly Birefringent
Twinning: Yes

14. Corundum in PP Light

15. Ruby
A ruby is a pink to blood-red
coloured gemstone, a variety
of the mineral corundum.
Its name comes from ruber,
Latin for red.
The brightest and most
valuable "red" called pigeon
blood-red, commands a huge
premium over other rubies of
similar quality.
Found in Myanmar, Thailand,
India, Pakistan, Afghanistan,
Sri Lanka, Madagascar,
Nepal and recently

16. Sapphire
Sapphire is a gemstone variety of the
mineral corundum, an aluminium
oxide, when it is a colour other than
red or dark pink.
Trace amounts of other elements such
as iron, titanium, or chromium can give
corundum blue, yellow, pink, purple,
orange, or greenish color.
Name derived from Greek sappheiros,
meaning "blue stone“.
Found in Australia, Thailand, Sri
Lanka, Madagascar and US.

17. Pink, Padmaraga and Star Sapphires

18. Emerald
Emerald is a variety of the mineral
beryl coloured green by trace
amounts of chromium and
sometimes vanadium.
The word "Emerald" is derived from
either the Hebrew word izmargad
meaning "green“.
Found in Afghanistan, Australia,
Austria, Brazil, Bulgaria, Cambodia,
Canada, China, Egypt, Ethiopia,
France, Germany, India, Italy,
Kazakhstan, Madagascar,
Mozambique, Namibia, Nigeria,
Norway, Pakistan, Russia, Somalia,
South Africa, Spain, Switzerland,
Tanzania, United States, Zambia
and Zimbabwe.

19. Emerald (Beryl)
Colour: Blue-green
Streak: White Hardness: 7.5 – 8
Cleavage: Very Poor Fracture: Even Luster:
Vitreous
Specific Gravity: 2.7 - 2.9 Transparency:
Translucent
Crystal System: Hexagonal
Crystal Habit: Hexagonal Prisms

20. Emerald: Optical
Properties
Colour: Colourless
Relief: Low to Moderate
Pleochlroism: Yes
Uniaxial (negative)
Birefringence: Low, first order grays
Cleavage: At right angles

21. The Gachala Emerald

23. Tourmaline
Tourmaline is a crystal boron
silicate mineral compounded with
elements such as aluminium, iron,
magnesium, sodium, lithium, or
potassium. Tourmaline is
classified as a semi-precious
stone and the gem comes in a
wide variety of colors.
The name comes from the
Sinhalese word "Thuramali“, or
"Thoramalli“, which applied to
different gemstones found in Sri
Lanka.
Found three most US, Czech Republic,
The in Sri Lanka, well-known Pink Tourmaline (Elbaite) in
membersAfrica Elbaite, Schorl,
Brazil, are and Afghanistan Quartz

24. Tourmaline
Color: Black, brown, green, red, pink, blue, and
gray.
Streak: White
Luster: Resinous
Transparency: Transparent to Opaque; usually
Translucent
Hardness: 7 - 7.5
Crystal System: Hexagonal
Habit: Deformed Triangular Prisms
Cleavage/Fracture: Poor/Conchoidal to Uneven

25. Tourmaline: Optical
Properties
Colour: Colourless
Pleochlorism: Yes
Relief: High
Uniaxial (Negative)
Cleavage: None but prominent cracks visible
Parallel extinction
Lower 2nd order to lower 3rd order interference
colours.

26. Tourmaline in PP and XP light

27. Thermochromism: The
colour of some Tourmaline
can be enhanced through
heat treatment. Some
greenish stones can be
made deep green, some
brownish-red stones can be
made red, and some light
pink stones can be made
colourless through heating.
Tourmaline can form in
extremely aesthetic slender
crystals that are highly
valued by collectors.
Chatoyant variety used as
cat’s eye.

28. Quartz
Quartz is the second-most-
abundant mineral in the Earth's
continental crust, after feldspar.
There are many different
varieties of quartz, several of
which are semi-precious
gemstones. Especially in
Europe and the Middle East,
varieties of quartz have been
since antiquity the most
commonly used minerals in the
making of jewellery and
hardstone carvings.
Gemstone variety mostly found
in US and Brazil.

29. Quartz
Colour: Colourless, Milky, Purple, Pink, Yellow,
Brown
Streak: White Specific Gravity: 2.65 Hardness: 7
Cleavage/Fracture: None/Conchoidal or Brittle
Luster: Vitreous Transparency: Transparent to
Opaque
Crystal Shape: Hexagonal
Crystal Habit: Prismatic/Massive

30. Quartz- Optical Properties
Colour: Colourless
Cleavage: None
Relief: Low
Uniaxial (positive)
Birefringence: Low with first order greys and whites

31. Quartz in PP and XP Light

32. Onyx and Agate

33. Tiger’s Eye
Tiger's eye is a chatoyant
gemstone that is usually
a metamorphic rock that
is a golden to red-brown
colour, with a silky luster.

34. Egg shape tiger's eye with iron stripes

35. Olivine
The mineral olivine (when gem-
quality also called peridot) is a
magnesium iron silicate. It is a
common mineral in the Earth's
subsurface but weathers quickly on
the surface.
Found in Pakistan, Nepal,
Myanmar, Russia, Italy and Norway

36. Olivine
Colour: Colourless, Olive Green, Greenish Yellow,
Grey
Streak: White Specific Gravity: 3.1 -3.4 Hardness:
5.5 - 6.5
Cleavage/Fracture: Poor/Conchoidal
Luster: Vitreous Transparency: Translucent
Crystal Shape: Orthorhombic
Crystal Habit: Prisms and Dipyramids

37. Olivine - Optical Properties
Colour: Colourless to faint green
Cleavage: None
Relief: High
Biaxial
Birefringence: High with mostly third order colours

38. Olivine in PP and
XP light

39. Olivine
Olivine is named for its
typically olive-green
colour (thought to be a
result of traces of nickel),
though it may alter to a
reddish colour from the
oxidation of iron.
Extraterrestrial
occurrence

40. Zircon
Zircon is a mineral belonging to the group of
nesosilicates. Its chemical name is zirconium silicate.
The natural colour of zircon varies between colourless,
yellow-golden, red, brown, blue, and green. Colourless
specimens that show gem quality are a popular substitute
for diamond; these specimens are also known as "Matura
diamond".

41. Zircon
Colour: Colourless, Brown, Green, Grey, Red
Streak: Colourless - White Specific Gravity: 4.68
Hardness: 7.5 Cleavage/Fracture:
Poor/Conchoidal
Luster: Adamantine
Transparency: Transparent- Translucent
Crystal Shape: Tetragonal
Crystal Habit: Square Prisms, Pyramids or a
combination of the two

42. Zircon - Optical Properties
Colour: Colourless to faint green
Cleavage: Imperfect
Relief: Very High
Birefringence: High with mostly third to fouth order
colours in Prismatic Sections
Uniaxial (Positive)
Basal Sections are isotropic

43. Zircon in PP and XP
Light

44. Imitations and Artificial
Gemstones
Some gemstones are manufactured to imitate other gemstones.
They are called imitations.
The imitations copy the look and colour of the real stone but
possess neither their chemical nor physical characteristics.
Lab created gemstones are not imitations. Synthetic (lab
created) corundums, including ruby and sapphire, are very
common and they cost only a fraction of the natural stones.
Whether a gemstone is a natural stone or a lab-created
(synthetic) stone, the characteristics of each are the same.
Lab-created stones tend to have a more vivid colour to them, as
impurities are not present in a lab and do not modify the clarity
or colour of the stone.

45. Thank you!