Column: The secret world of sapphires and rubies

Published 10:37 am Thursday, February 1, 2007

By Staff
If, after reading last week's column about Bill Smith and his gem stones, you thought I might be going somewhere with that, you're right.
As nature enthusiasts, we marvel at trees, plants, birds and animals, but very few of us have ventured into the equally fascinating world of rocks and minerals. The royalty of all the rocks are, of course, the ones we call gems.
There are dozens of stones we especially prize for their beauty, but only four rank as truly precious gems – diamonds, rubies, sapphires and emeralds. All the other beautiful stones we adorn ourselves with, opal, topaz, garnet, aquamarine and infinitum are referred to as semi-precious. The four precious gems are held in such high esteem because of three factors, beauty, rarity and durability. Many semi-precious gems equal or even exceed the elite four in the beauty department but are more common or can be more easily damaged.
Diamonds have received so much publicity that most of us know the basics concerning them. You don't hear much about the other three, though, even though they're often priced higher than diamonds.
This week, we'll take a peak into the secret world of sapphires and rubies, one of the oldest gems prized by man. I can lump these two together because they are actually the same thing, just differently colored.
Sapphires and rubies are the second hardest naturally occurring material, the hardest being diamond. They are made of aluminum oxide, also called corundum, which is aluminum's equivalent of rust. Imagine that, your screen door and lawn chairs are coated with sapphires. Corundum is widely used as an abrasive for sandpaper and grinding compounds. Pure corundum is colorless. It's when slight amounts of other materials are added during the cooking process that the various colors occur. Sapphires are most often dark blue to black, which is caused by iron and titanium. However, other impurities produce a variety of colors from yellow to green, orange, purple or most anything else but red. When Ma Nature adds chromium to the recipe the sapphire is red, which makes it a ruby, the most highly prized color of all.
You've surely heard of star rubies and sapphires, but probably never seen one. These occur when rutile crystals are present. The rutile forms a six pronged, luminescent star encompassing the entire stone when it is cut in a rounded dome shape.
It's mind boggling to think of the circumstances that must occur to create these gems and present them to us. Sapphires and rubies begin their formation miles underneath the earth's surface in Ma's bubbling stew pot. The corundum must come together in sufficient quantity and purity and then just the right amount of iron, titanium, chromium or whatever must happen along and be mixed in. There can be no other impurities or it's just another nondescript rock.
Then we need a volcano to transport this material to the surface so we can get at it. But that's only part of the equation. For the corundum to transform into a transparent gem the eruption must be hot enough for the magic temperature yet surface slowly enough to provide proper aging. The sapphire brew must also be at the front of the erupting material to be blown out with the volcanic ash, otherwise it would get stuck far below the surface. If any of these factors are less than perfect you have, well, sandpaper.
No wonder they're so rare. Another factor contributing to rarity is the minerals that give the stones color tend to cause cracks and fissures, which renders the stone worthless.
A couple of centuries ago we found that heating lesser quality stones nearly to their melting point clears them up and enhances the color. This is common practice today. Don't confuse this with synthetic stones, which are entirely man made, sometimes by an old man on his back porch with an arc welder.
Sapphires and rubies occur all over the globe but most come from India eastward to Thailand, Burma and Sri Lanka. More recently parts of Africa have become a major supplier as well. A few are found here in the U.S., primarily Montana and North Carolina. Carpe diem.