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Monday, 25 August 2014
RUBY - The Undisputed King of Gemstones (Part-1)
Red is an interesting color
with which we correlate our intense emotions. On one hand red denotes
happiness, love and passion. On the other hand it signifies obsession,
jealousy, anger and fear. Thus, we can say that red is the color of life! Ruby
is a gemstone which showcases this color of life and that is why it is termed
as the ratnarajor King of Gemstones.
Ruby has been one of the most
prized gemstones throughout the history because of its beautiful scarlet hues,
its durability and rarity. It has been mentioned of in various sacred texts.
Rubies with vivid red hues and large sizes can sometimes claim higher prices
than diamonds. The Indian name for ruby is Manak/Manik and it represents Sun in
astrology. It is the birth stone for the month of July.
In this post various aspects
such as properties, ideal ruby color, ancient and current day sources,
inclusions (natural, synthetic and treated rubies) and imitations will be
PROPERTIES: ruby is the most
desirable variety of the mineral group Corundum. It belongs to hexagonal
crystal structure and is rated at number 9 on Mohs hardness scale. The refractive
index of ruby is 1.76-1.77 with a birefringence of .008-.010. Corundum
varieties are made of aluminium oxide. In its purest form corundum is
colorless. The trace element which is responsible for ruby’s color is chromium.
Rubies are formed in two types of deposits:
Marble hosted: in this deposit
the host rock is marble and these rubies have less or no iron causing them to
fluoresce in long wave UV light. These deposits are usually found in Myanmar,
Vietnam and the Himalayas.
MARBLE HOSTED RUBY
Basalt hosted: in this deposit
the host rock is basalt. These rubies have higher iron content giving them a
brownish appearance. These rubies show faint or no fluorescence in UV light.
These rubies are usually heat treated to improve their color. Basalt hosted deposits
are formed mostly in Thailand and Cambodia.
BASALT HOSTED RUBY
Ruby displays pleochroism
under a dichroscope. It shows two distinct tones- orangy red and purplish red
and specific gravity of ruby is 4.
COLOR: the factor that has the
strongest influence on the market value of a ruby is its color. The intensity
or the saturation of ruby’s color is dependent on the chromium content. Higher
the content, higher is the saturation of ruby.
“Pigeon blood” is the term usually associated
with fine ruby color. Fine color displays vivid red hues (primary hue) with
hint of orange or purple (secondary hue) in it. As the intensity of secondary
hues increases, the value of ruby declines. Tone is a very important factor to
consider when judging the color of a ruby. If the tone is too light then it
might be considered as a pink sapphire rather than a ruby. Similarly if purple
or orange is too dominant in a corundum stone it will be termed as purple and
orange sapphire respectively. It is often very difficult to draw a line between
ruby and pink sapphires and the topic has been highly debatable.
SOURCES: The most important
historic source of ruby is Mogok in Myanmar. The rubies in this region are
marble hosted, display a striking deep red body color and fluoresces red under
UV light. Rutile silk is the most dominant inclusion in Mogok rubies.
The second most important
source which has provided good commercial quality rubies to the market is Mong
Shu in Myanmar. The rubies from this region are also marble- hosted but
generally have an extremely saturated color with a red rim. These rubies are
usually heat treated for improved appearance. After the treatment the natural
inclusions are usually distorted.
Political unrest in Myanmar leads to irregular
production and supply. Though it is the most important source of ruby mining
but these factors limit the miners to exploit the potential mines completely.
MINING IN MYANMAR
Thailand is also amongst
world’s major ruby sources. It is the largest trading and cutting centre for
rubies. Thai rubies are basalt-hosted and hence brown in color and lack
fluorescence. These rubies are heat treated for improved appearance. Ruby
deposits are spread all over Thailand but the most commercially viable sources
are in the Chantaburi. Cambodia is also an important ruby source.
Sri Lanka has corundum bearing
deposits and they mostly produce pink sapphires, blue sapphires and other fancy
colors. Vietnam is also a very promising source of ruby. In Africa, Kenya
sometimes can produce fine color rubies. Afghanistan, Pakistan and Nepal also
have ruby bearing deposits but mostly suitable for cabochons.
Part-2 of this article will
cover interesting topics like inclusions of natural, synthetic and treated
rubies and imitations.
*The Author is a Colored Stone Graduate from Gemological Institute of America, Mumbai and a Diamond Graduate from Solitaire Diamond Institute, Bangalore. She also holds a Diploma in Jewelry Designing & Manufacturing from Jewelry Product Development Centre, Jaipur. She also blogs at 'The Jewel Affair'