Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Michelle Guilmette
Rainbow of Sapphires
When I think of the gem Sapphire, my mind immediately goes to the color blue. I
think of a true blue that has a brilliance hard to match. Sapphire also happens
to be the color of a deep blue Crayola crayon! I believe that many people think
that blue is the only color of sapphire. This thought would make sense because a
blue sapphire, also called corundum due to the mineral class that is belongs to,
is the most widely available color. However, sapphires come in a wide range of
colors: corundum, while a blue mineral, is the main make up of all the other
colors excluding red.
On Moh’s scale of hardness, all sapphires register at level 9. Sapphires are a combination of aluminum and oxygen, Al2O3. They are popular worldwide due to their beauty, as well as their durability. Sapphires are found in India, Burma, Ceylon, Thailand, Vietnam, Australia, Brazil and Africa. There are three different terms that are used to describe sapphires (similar to the 4 C’s of Diamonds).
· Hue – describes the basic color, such as blue, slight green, strong pink, light purple
· Saturation – describes the extent in which the hue is masked, or tinted, by brown or gray
· Tone – describes the amount of color in the gem from very slight to very dark
Sapphire hues range from slight green to strong purple. Blue, as mentioned earlier, is the ideal color hue. A vivid saturation is ideal for a sapphire and a medium tone is considered perfection.
Transparency, while not one of the three main definitions, is also a way to determine the quality of a sapphire. Ideally, a sapphire is completely transparent; opaque sapphires are avoided the majority of the time in regards to sales.
As shown in the chart below, medium to dark, vivid, blue sapphires are the most
desirable and are considered the best quality. Dark or gray areas in the gem are
called extinction. Extinction is undesirable and affected by the cut, quality,
and tone of the gemstone.
In order to achieve the above traits and have the desired color of blue, some sapphires are heat treated. When a sapphire is heated at extremely high temperatures, 1500 degrees Celsius and higher, the impurities in the gem change chemically. This chemical change allows for a purer color and a higher quality sapphire. In fact, this treatment can change a colorless sapphire into a strong blue sapphire! Consequently, when heated at lower temperatures, a sapphire’s saturation can be lightened.
While the blue sapphire is the most popular, sapphires come in a large array of
colors to include colorless and very strong blue, almost black. The red variety
corundum is the only color excluded; these red gems are referred to as rubies.
Padparadscha sapphires are extremely rare and prized sapphires from Sri Lanka
and Vietnam. Padparadscha is a combination of two Sanskrit words, lotus and
color, due to the comparison of the color to that of a lotus flower. The color
is a stunning medium toned pink-orange. This gem is one of the only varieties of
sapphires that can reach more per carat than the blue variety. These rare jewels
are typically priced around $20,000 per carat!
Another rare sapphire is the pink variety. These gems range from light pink to a strong pink hue and the more brilliant the tone and hue, such as a hot pink, the pricier the gem tends to be. These gems are found primarily in Burma and Sri Lanka.
Violet sapphires are in the hue between the popular blue and pink. These gems
are mainly mined in Sri Lanka and Africa. Violet, or purple, sapphires are rare
when over one carat and can cost about $5,000 per carat.
Yellow sapphires are mined primarily in Sri Lanka. Their natural color is
typically a pale yellow, but some hues are deeper and more brilliant. However,
most deep yellow tones have been heat treated.
Green sapphires are primarily found in Africa, specifically Tanzania and Zambia,
but they can also be found in Australia. The purest green sapphires are very
rare and have mostly been found in Sri Lanka. The green sapphires range from a
yellow-green hue to a bright green similar to the color of an emerald.
Sapphires have stood the test of time. The sapphire is rumored to have been the
tablet on which the Ten Commandments were written upon, making it a sacred
gemstone. Sapphires historically belonged to the rich because of the healing and
calming powers they once were believed to possess. Throughout the ages,
sapphires have been a symbol of wisdom, virtue, fidelity, good fortune, and
holiness. The sapphire is a popular choice as an engagement gem, symbolizing the
faithfulness and sincerity of the proposal of marriage. Sapphires are also where
we get the term ‘True Blue.”
Through all the colors and varieties of this brilliant gem, the sincerity and
depth of the stone never fails. Whether blue, pink, or yellow, sapphires never
fail to please and astonish jewelers and jewelry fans alike. The natural, rare
form of this sapphire is a treasure one cannot describe with words.
Pictures 2-8, 10, 12-13: http://www.gemnation.com/base?processor=getPage&pageName=sapphire_education
Pictures 9, 14-15: