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In the gem trade,
sapphire refers to the blue variety of corundum. However, excluding
red ruby, it scientifically encompasses all
other gem varieties of corundum. (In essence, ruby is really a red
sapphire, since ruby and sapphire are identical in all properties
except color.)
Sapphire is the most precious of blue gemstones. It is a most
desirable gem due to its color, hardness, durability, and luster.
The most valuable color of sapphire is cornflower blue, known as
Kashmir sapphire or Cornflower blue sapphire.
Until the last century,
all sapphires (excluding blue) were called the same name as a
popular gemstone of that color with the prefix "oriental" added to
it. For example, green sapphire was known as "oriental emerald". The
practice of applying the name of a different gemstone to identify
the sapphire was misleading, so these names were virtually
abolished. What was once called "oriental emerald" is now called
"green sapphire". The same holds true for all other color varieties
of sapphire. However, the word "sapphire" in its plain context
refers only to blue sapphire, unless a prefix color is specified.
Sapphire with a color other than blue is often called a "fancy" in
the gem trade.
Inclusions of tiny,
slender, parallel Rutile needles cause polished sapphire gems to
exhibit asterism. Sapphire gems displaying asterism are known as
"star sapphires", and if transparent are especially prized. Star
sapphires are usually in six ray stars, but twelve ray stars are
also known. Very rarely, sapphire also exhibits cat's eye effect.
Color zoning, which forms from growth layers that build up during
the formation of the stone, is present in certain sapphires.
However, uniformity of color is an important factor in a sapphire's
value.
Colorless and pale blue
sapphires from certain localities may be heat-treated to give them
an intense blue color. Heat-treatment may also improve the clarity
of some sapphires by removing tiny inner inclusions. Sapphire is
pleochroic, displaying a lighter and more intense color when viewed
at different angles. Some pleochroic sapphire is blue when viewed at
one angle, and purple at a different angle.
A rare variety of
sapphire, known as color changing sapphire, exhibits
different colors in different light. In natural light, color
changing sapphire is blue, but in artificial light, it is violet.
This effect is the same phenomenon seen in alexandrite.
Sapphire was first
synthesized in 1902. The process of creating synthetic sapphire is
known as the vernueil process. Only experts can distinguish
between natural and synthetic sapphire.
Sapphire is a tough and
durable gem, but it is still subject to chipping and fracture if
handled roughly.
VARIETIES
Kashmir Sapphire -
Sapphire with a distinct velvety-blue color
Cornflower Sapphire - Synonym of
Kashmir sapphire (above)
Cornflower Blue Sapphire -
Synonym of Kashmir sapphire (above)
Star Sapphire - Sapphire displaying
asterism
Padparadschah - Orange-pink
variety of sapphire
Color Changing Sapphire -
Sapphire exhibiting a different color in natural and artificial
light
Bi-colored Sapphire - Sapphire
with more than one color
Cat's Eye Sapphire - Sapphire
exhibiting cat's eye effect
Fancy Sapphire - Any sapphire with a
color other than blue
Verneuil Sapphire - Synthetic,
laboratory-grown sapphire
Nowadays, sapphire is classified by its color in the gem trade (i.e.
green color sapphire is "Green Sapphire"). Colorless sapphire is
usually called "White Sapphire".
The "oriental" prefixes are not used anymore, but they are still
occasionally seen. Below is a list of all the "oriental" sapphires:
Oriental Topaz - Straw yellow,
gem quality sapphire
Oriental Emerald - Light to
dark green, gem quality sapphire
Oriental Amethyst - Violet
to pink, gem quality sapphire
Oriental Peridot -
Yellow-green, gem quality sapphire
Oriental White Sapphire
- Colorless, gem quality sapphire
Some other (rarely used)
variety names:
Australian Sapphire - Dark blue to
nearly black sapphire
Bengal Amethyst - Purple
sapphire
Blue Alexandrite - Synonym
of color changing sapphire
Burma Sapphire - Synthetic,
laboratory-grown blue sapphire
Burmese Sapphire - Synonym of Burma
sapphire (above)
Ceylon Sapphire - Light blue sapphire
Indian Topaz - Yellow to
yellow-brown sapphire
King Topaz - Yellow to
yellow-brown sapphire
Rose Kunzite - Synthetic pink
sapphire
Star Topaz - Yellow star sapphire
Ultralite - Blue sapphire
Facts about Yellow
Sapphire
|
Color |
Blue,
yellow, green, white, colorless, pink, orange, brown, and
purple |
|
Hardness |
9 |
|
SG |
3.9 - 4.1 |
|
RI |
1.76 -
1.77 |
|
DR |
.0008 |
|
Luster |
Vitreous
to adamantine |
|
 |
|
Mineral
class |
Corundum |
|
Composition |
Be3Al2SiO6 |
|
