AZGem Gems
August, 2004
The World's Most Useful
Gem & Jewelry Monthly Newsletter

Written by Carolyn Doyle for customers of
The Dorado Company
and other visitors to the website who subscribe.


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Usable Gems... and a little opinion.


Corundum is King

Corundum is a mineral composed of two elements, aluminum and oxygen (aluminum oxide).

In its pure form, corundum is colorless... but if a few parts per million of other elements are added, corundum can become very colorful.

Corundum can occur in single crystals or in massive form (no particular shape).

It's the second hardest natural substance known. In industrial quality it's used as an abrasive, on sandpaper and such. (Diamond is four times harder.)

Our interest in this mineral is as a gemstone, of course, and it's two of the great gems.

Specific variety names are used when referring to the various types of corundum:

  • Sapphire
  • Ruby
  • Padparadscha (or padparadcha)
  • Aluminum oxide
  • Emery

The name corundum when used alone is applied to a brown, opaque variety of the mineral. It's used as an abrasive, after being crushed into small particles.

Emery, a black, massive variety of the mineral corundum is also used as an abrasive, after being crushed into small particles.

Gemstone Names

Ruby is used only for the red variety of corundum... not pink, and not orange. Where are the dividing lines between these colors? It's in the eye of the beholder, or I should say, the buyer!

Sapphire is used to denote blue sapphire. The  word sapphire comes from an ancient word for the color blue.

Padparadscha denotes a sapphire that is the color of a lotus blossom, a unique pink - orange color mix.

Other colors of sapphire use the particular color in the name. For instance there's:

  • Teal (blue-green) sapphire

  • Pink sapphire

  • Orange sapphire

  • Yellow sapphire

  • Gold sapphire

  • Green sapphire

  • Purple sapphire

  • Violet sapphire

  • White sapphire

  • Black sapphire

As a group, these are known as fancy colored sapphire.

Gem Color Causes

Enough about names, lets talk colors.

As mentioned above, if a few atoms of one or more other elements find their way into the crystal structure while the crystal is forming, magic can occur.

Corundum can then take on beautiful colors.

Ruby contains both chromium and iron, while blue sapphire is the result of trace amounts of titanium and iron.

Padparadscha contains manganese and chromium.

Pink sapphire contains vanadium and chromium, while orange sapphire is colored by vanadium and iron.

Yellow sapphire usually contains only iron as a coloring agent, but more deeply colored gold sapphire contains chromium and iron.

Green sapphire contains iron as its coloring agent, but less iron than yellow sapphire.

Got all that? It'll be an open book quiz. But first, a few more words about sapphire colors.

As you would expect, mixtures of these coloring agents will cause other colors such as teal, purple, and violet.

White sapphire is actually colorless and transparent. It's often used in earrings instead of diamonds.

Black sapphire is usually very dark green - blue - brown when a light is shined through it. This material is inexpensive, and is used as a more desirable and durable stone than onyx.

Star sapphires contain the mineral rutile. Rutile naturally orients itself at 60 degree angles when hosted in a sapphire crystal. Light reflecting off the rutile shows as a six-rayed star when properly cut.

Color change sapphires are a bit of magic. They change color, depending on whether they're being viewed in sunlight or incandescent light. The colors are often purple to pink, but a variety of other color combinations occur.

Gem Treatment

Sapphire and ruby are often treated to absorb  inclusions or enhance color. Heat treatment is very common, but X-ray and diffusion-treated sapphire are also available.

Deep diffusion treatment drives additional coloring agent into light colored stones. Blue and pink sapphires are successfully treated this way. The resulting gems are significantly less expensive than comparably colored, heat treated gems.

Diffusion treatment using beryllium as the coloring agent results in pink-orange sapphire.

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Some rubies and sapphires aren't treated at all. Here's a photo of some blue sapphire rough we received from Africa recently.

Important ruby mining locations are in Myanmar (Burma), Afghanistan, Thailand, Madagascar, and recently, in Tanzania.

Important sapphire mining locations are in Sri Lanka,  India, Pakistan, Thailand, Cambodia, Australia, and several African countries.

We have ruby, blue sapphire, and fancy colored sapphire in stock. Send me an email about the gem you're interested in and I'll tell you what I have in stock that day.

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Industry News...

Magnificent Jewels Auction

The recent gem and jewelry auction at Christie's Geneva offices saw the sale of two impressive colored stones: more than $100,000 per carat was paid for a 9.35-carat unheated Burmese ruby, and a private collector spent over $35,000 per carat for a 27.54-carat Kashmir sapphire.

Of primary Interest in colored stones sales, however, was the sale of a magnificent Burmese ruby and diamond necklace designed by Cartier in 1937 for the Maharaja of Nawanagar selling for more than $2.3 million.

The absence of a buyer for the 486.52-carat "Blue Giant of the Orient" sapphire caused temporary disappointment in the auction room, but Christie's was able to sell it immediately after the auction for $1 million.

More than 88 percent of the lots offered sold... for a total of $28.5 million.



Jewelry Dealers

The holidays are coming!

Are you making up new pieces of jewelry to rebuild and upgrade your inventory? Now is a good time to work at this fun and vital task.

We've recently received some new emerald, morganite, sapphire, peridot, and chrome diopside from our cutters.

As usual, all these gems are in sizes appropriate for center stones in  rings  and pendants.

Send me an email for information on gems that interest you.


Jewelry Dealers Program

Do you enjoy jewelry and gems?

Do you enjoy talking with friends and co-workers?

Take a look at our great Jewelry Dealers Program.

Carolyn Doyle

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The Dorado Company
P.O. Box 8232
Scottsdale, AZ 85252-8232