The World's Most Useful
Gem & Jewelry Monthly Newsletter
Written by Carolyn Doyle for customers of
The Dorado Company
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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
Corundum can occur in single crystals or in massive form (no
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:
- Padparadscha (or padparadcha)
- Aluminum oxide
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.
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
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:
As a group, these are known as fancy
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
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
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
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.
Some rubies and sapphires aren't treated at
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.
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
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.
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
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The Dorado Company
P.O. Box 8232
Scottsdale, AZ 85252-8232