C is for Corundum
Corundum is a naturally occurring aluminum oxide mineral. What? What does that mean? Second only to a diamond, it is the hardest mineral, registering a hardness of 9 on the Mohs scale. Similar to Beryl, the mineral forms gemstones of different colors by the presence of other elements such as chromium or iron and titanium.
Chromium produces a red color and results in the gemstone we commonly know as a ruby. Rubies are the designated birthstone for the month of July. Their vibrant red color makes a gorgeous gem. There are some amazing specimens at the Smithsonian. Click here to view.
Iron and Titanium produce a blue color which results in the gemstones known as a sapphires.
When I was growing up, sapphires (especially a star sapphire) were a much sought after gemstone for rings and pendants. My mother often talked about wanting a star sapphire.
Just what is a star sapphire? An asterism (star effect) is formed when a sapphire containing streaks of the mineral rutile are ground into a rounded cabochon. Under light, a star-like shape of light is reflected back to the eye.
There are various colors of sapphires but the deep blue is the most desirable. Any color of sapphire other than red, blue, or clear (and there is a wide range of colors) are called fancy sapphires.
You may not own a ruby or a sapphire, but you might own an emery board. Emery is a mineral containing corundum which has been used as an abrasive for many years. Most emery is made synthetically now, from the mineral bauxite.
Rubies are used in lasers and in ‘jewel movements’ for Swiss watches due to the mineral’s hardness and resistance to wear.
The mineral corundum is synthetically created now and used in the manufacture of every day items such as the glass on grocery store scanner windows, telescopes, and aircraft windows. As you can see, the uses of corundum are vast.
This is a good time to talk about the ethical concerns of gem mining. The majority of rubies today come from Myanmar, the sale of which helps fund corruption in their government. As a result, jewelers in the U.S. are not allowed to import from Myanmar.
The same held true for diamond mining which helped coin the phrase ‘blood diamonds’. Efforts to track diamonds and ensure they are not ‘conflict diamonds’ have had less than stellar success.
In addition, individuals who work in many of these countries as miners or stone cutters, are not provided with the necessary safety equipment. Many are sick from silicosis.
Now, let’s talk pricing again. Quality rubies 6x9mm run from $238 – $49,000 depending on quality. Sapphires $360 to $4,800 for a 1 carat stone. I can buy a 4mm Ruby AA quality for $75 (both filled and heat treated). A similar size heat treated sapphire would also cost about $75. Star sapphire stones are difficult to pinpoint from a reliable source. I would say this is a perfect case of buyer beware.