Gem Profile- Corundum
Corundum
Many years ago, when developing wire jewelry techniques began taking over my life, I decided that the best way to keep my brain in "rock mode" was to study a different mineral about every 6 months. I happen to live close to an area of the United States that is rich in corundum, so it became my first subject. Like several other minerals that I will eventually profile, corundum has been known about and used for a very long time so there is a lot of information available.
Many years ago, when developing wire jewelry techniques began taking over my life, I decided that the best way to keep my brain in "rock mode" was to study a different mineral about every 6 months. I happen to live close to an area of the United States that is rich in corundum, so it became my first subject. Like several other minerals that I will eventually profile, corundum has been known about and used for a very long time so there is a lot of information available.
For just the basics about corundum, Wikipedia has a nice article on Corundum.
I like that Wikipedia is an easy way for people to get a snapshot of a subject matter; personally, I prefer good reference books and when possible, being able to actually hold the material in my hand. My article is going to touch on just some of corundum's amazing highlights.
26mm x 21mm x 10mm lab-created oval Pink Sapphire, wire wrapped and hung on keishi pearls by Julia McCormack.
I like that Wikipedia is an easy way for people to get a snapshot of a subject matter; personally, I prefer good reference books and when possible, being able to actually hold the material in my hand. My article is going to touch on just some of corundum's amazing highlights.
26mm x 21mm x 10mm lab-created oval Pink Sapphire, wire wrapped and hung on keishi pearls by Julia McCormack.
Sapphire and ruby crystals. Some have polished windows to show their star potential, or not. Private collection, Dale Armstrong.
Corundum's Physical Properties
Corundum is a crystalline mineral composed of aluminum oxide ($Al_2O_3$). It has a Mohs hardness of 9, making it second in hardness only to diamond.Pure corundum is typically described as white or silver.
Its trigonal crystals can be opaque, transparent, or translucent.When forming near other minerals, corundum takes on a spectrum of colors every shade of orange, yellow, green, blue, violet, white, black, and pink.In the jewelry industry, these colored stones are known as Sapphires.
Any color other than deep pink or red can be marketed as a "fancy sapphire."When the color is a deep pink or red hue, the material is called Ruby.
Ruby and the blue sapphire have long been listed among the top three traditional gemstones, along with emerald.Special A natural sapphire with an orange-pink color carries a special label.
This is nicely explained by David Federman in his book, Modern Jeweler's Consumer Guide to Colored Gemstones.
Corundum is a crystalline mineral composed of aluminum oxide ($Al_2O_3$). It has a Mohs hardness of 9, making it second in hardness only to diamond.Pure corundum is typically described as white or silver.
Its trigonal crystals can be opaque, transparent, or translucent.When forming near other minerals, corundum takes on a spectrum of colors every shade of orange, yellow, green, blue, violet, white, black, and pink.In the jewelry industry, these colored stones are known as Sapphires.
Any color other than deep pink or red can be marketed as a "fancy sapphire."When the color is a deep pink or red hue, the material is called Ruby.
Ruby and the blue sapphire have long been listed among the top three traditional gemstones, along with emerald.Special A natural sapphire with an orange-pink color carries a special label.
This is nicely explained by David Federman in his book, Modern Jeweler's Consumer Guide to Colored Gemstones.
What about Corundum that's not Suitable for Jewelry?
Corundum that is not gem quality is most often found in metamorphic or igneous rock formations.
Due to its hardness, it is frequently used to make emery and abrasive grinding products.
Most gem-quality corundum is found in alluvial gravel deposits (scraped and left by glaciers).
This is because the stone is both hard enough to withstand abuse and very heavy, which makes it easy to pan for.
I search for corundum in locations like Mitchell County, North Carolina.
Corundum can be found across North America, with Montana and North Carolina being the best-known sources.
It is also found in Russia, Australia, Thailand, and Africa.
A lot of gem-quality material comes from mines in India.
It is interesting that these two well-known gemstones, Ruby and Sapphire, are actually the same mineral, with color being the only difference.
Perhaps the separation occurred during corundum's long history of use as personal ornaments, jewelry, statues, and icons. The stones were often chosen by color for various reasons, some of which follow below.
Corundum that is not gem quality is most often found in metamorphic or igneous rock formations.
Due to its hardness, it is frequently used to make emery and abrasive grinding products.
Most gem-quality corundum is found in alluvial gravel deposits (scraped and left by glaciers).
This is because the stone is both hard enough to withstand abuse and very heavy, which makes it easy to pan for.
I search for corundum in locations like Mitchell County, North Carolina.
Corundum can be found across North America, with Montana and North Carolina being the best-known sources.
It is also found in Russia, Australia, Thailand, and Africa.
A lot of gem-quality material comes from mines in India.
It is interesting that these two well-known gemstones, Ruby and Sapphire, are actually the same mineral, with color being the only difference.
Perhaps the separation occurred during corundum's long history of use as personal ornaments, jewelry, statues, and icons. The stones were often chosen by color for various reasons, some of which follow below.
Ruby
In some cultures, it was believed that ruby could make a person invulnerable.
Early Burmese warriors often placed thin slabs of ruby under their skin before going into battle.
Ancient people called any pretty red or reddish-pink rock "ruby."
As a result, some "ruby" artifacts are now identified as spinel, which belongs to a separate mineral group.
In 1912, the Jewelers of America adopted their Modern Gemstones list.
On this list, ruby is associated with those born in July and the constellation Capricorn.
In ancient Sanskrit, ruby was originally called Ratanraj, which means "King of Gems."
Ruby has been used throughout the ages as a symbol of love, passion, and power.
It is also the traditional stone for both the 15th and 40th wedding anniversaries.
Wire jewelry made using lab-grown rubies by Dale Cougar Armstrong.
In some cultures, it was believed that ruby could make a person invulnerable.
Early Burmese warriors often placed thin slabs of ruby under their skin before going into battle.
Ancient people called any pretty red or reddish-pink rock "ruby."
As a result, some "ruby" artifacts are now identified as spinel, which belongs to a separate mineral group.
In 1912, the Jewelers of America adopted their Modern Gemstones list.
On this list, ruby is associated with those born in July and the constellation Capricorn.
In ancient Sanskrit, ruby was originally called Ratanraj, which means "King of Gems."
Ruby has been used throughout the ages as a symbol of love, passion, and power.
It is also the traditional stone for both the 15th and 40th wedding anniversaries.
Wire jewelry made using lab-grown rubies by Dale Cougar Armstrong.
Blue Sapphire
Blue sapphire is the modern birthstone for those born in September and under the constellation of Taurus.
It is believed to protect a loved one from envy and symbolizes loyalty. It represents both the 5th and 45th wedding anniversaries.
Early Persians believed the Earth rested on a blue sapphire and that the sky was its reflection. Blue sapphire was also thought to prevent poisoning.
Like ruby, any pretty blue rock was often called a sapphire in early days, most often lapis lazuli.
Both ruby and sapphire are mentioned in the Bible as cabochons on the breastplate of the High Priest, Aaron. There are many other Biblical references to these gemstones, including a description of a foundation.
It is likely that the two distinct colors were originally thought to be two totally different materials.
If you are interested in more historical details about corundum, I recommend David Federman's book. He discusses the history of sapphires in well-written pages.
Left: 2 Pink Sapphires. Right: 4 Rubies. Notice the difference in the depth of color in these lab-grown fancy sapphires and rubies used in wire jewelry designs by Dale Cougar Armstrong.
Blue sapphire is the modern birthstone for those born in September and under the constellation of Taurus.
It is believed to protect a loved one from envy and symbolizes loyalty. It represents both the 5th and 45th wedding anniversaries.
Early Persians believed the Earth rested on a blue sapphire and that the sky was its reflection. Blue sapphire was also thought to prevent poisoning.
Like ruby, any pretty blue rock was often called a sapphire in early days, most often lapis lazuli.
Both ruby and sapphire are mentioned in the Bible as cabochons on the breastplate of the High Priest, Aaron. There are many other Biblical references to these gemstones, including a description of a foundation.
It is likely that the two distinct colors were originally thought to be two totally different materials.
If you are interested in more historical details about corundum, I recommend David Federman's book. He discusses the history of sapphires in well-written pages.
Left: 2 Pink Sapphires. Right: 4 Rubies. Notice the difference in the depth of color in these lab-grown fancy sapphires and rubies used in wire jewelry designs by Dale Cougar Armstrong.
Synthetic Corundum & Treatments
Corundum can be purified and reconstructed into synthetic ruby and sapphire.
These manmade stones are chemically and structurally identical to their natural counterparts.
Several methods are used today. The first was developed by Gaudin in 1837; you can read more about it in the Wikipedia corundum article.
Some people enjoy owning a flawless ruby or sapphire. Even though the stones are lab-grown, they are still valuable gemstones that test as pure material.
Synthetic corundum is super hard and durable, making it useful beyond jewelry. An example is the scanning screen at your local checkout register.
Unfortunately, because both natural ruby and sapphire are extremely precious, there have been countless controversies.
These controversies surround treatments used to perfect flaws in natural stones that are often sold without disclosing the treatments used.
Corundum can be purified and reconstructed into synthetic ruby and sapphire.
These manmade stones are chemically and structurally identical to their natural counterparts.
Several methods are used today. The first was developed by Gaudin in 1837; you can read more about it in the Wikipedia corundum article.
Some people enjoy owning a flawless ruby or sapphire. Even though the stones are lab-grown, they are still valuable gemstones that test as pure material.
Synthetic corundum is super hard and durable, making it useful beyond jewelry. An example is the scanning screen at your local checkout register.
Unfortunately, because both natural ruby and sapphire are extremely precious, there have been countless controversies.
These controversies surround treatments used to perfect flaws in natural stones that are often sold without disclosing the treatments used.
Starry Corundum
Many people wonder about star sapphires or star rubies. The basic corundum material is the same in these specialty stones.
The key difference is the position of tiny, needlelike included crystals. These are most often rutiles (titanium dioxide) that form within the corundum.
These rutiles are never found in a transparent specimen. They must be situated in an opaque corundum.
When the stone is properly oriented and cut, with a center junction, the rutiles reflect light. This reflection makes a six-pointed "star" appear to float on the stone's surface.
These star formations are difficult to find. They are even more challenging for a lapidary to cut properly to show the stone's best advantage.
that not all natural star corundum stones have exactly six points.
A star sapphire is known metaphysically as a "stone of destiny.
Custom-designed and created in 14kt solid gold for George McCannon, owner of The Old Pressley Sapphire Mine, by Dale Cougar Armstrong.
Many people wonder about star sapphires or star rubies. The basic corundum material is the same in these specialty stones.
The key difference is the position of tiny, needlelike included crystals. These are most often rutiles (titanium dioxide) that form within the corundum.
These rutiles are never found in a transparent specimen. They must be situated in an opaque corundum.
When the stone is properly oriented and cut, with a center junction, the rutiles reflect light. This reflection makes a six-pointed "star" appear to float on the stone's surface.
These star formations are difficult to find. They are even more challenging for a lapidary to cut properly to show the stone's best advantage.
that not all natural star corundum stones have exactly six points.
A star sapphire is known metaphysically as a "stone of destiny.
Custom-designed and created in 14kt solid gold for George McCannon, owner of The Old Pressley Sapphire Mine, by Dale Cougar Armstrong.
Most natural star sapphires used in jewelry making today are mined in India.
There is only one recognized mine for blue star sapphires in the United States, the Old Pressley Sapphire Mine in Canton, North Carolina.
Just over the mountain from my home, both the Cartier and Tiffany jewelry companies have mined the gorgeous Canton Cornflower Blue in past years.
Naturals: Black Star Diopside and Blue Star Sapphire. Private collection, Dale Armstrong.
There is only one recognized mine for blue star sapphires in the United States, the Old Pressley Sapphire Mine in Canton, North Carolina.
Just over the mountain from my home, both the Cartier and Tiffany jewelry companies have mined the gorgeous Canton Cornflower Blue in past years.
Naturals: Black Star Diopside and Blue Star Sapphire. Private collection, Dale Armstrong.
Many synthetic and simulated stones represent star sapphires on the market today.
These are often made from resin, plastic, or glass.
During WWII, an Ohio-based company called Linde Air Products began mass-producing synthetic corundum.
They named their product the "Lindy Star" sapphire.
From the 1940s through the 1950s, Union Carbide also produced a synthetic star ruby, which was also called a "Lindy."
The genuine Lindy Star cabochon was extremely popular for showy costume jewelry.
Today, these pieces are considered collector's items.
There is one other look-alike to mention: sometimes you will find what appears to be an affordable, natural, black star sapphire while shopping.
Look closely: it is more than likely a black star diopside. That specific stone will be the subject of a later gem profile!
Left: Ruby wrapped with bronze wire and hung on a garnet strand. Right: Emerald-cut Pink Sapphire (27mm x 23mm x 12mm) hung on a braided satin cord. Both wrapped by Julia McCormack.
These are often made from resin, plastic, or glass.
During WWII, an Ohio-based company called Linde Air Products began mass-producing synthetic corundum.
They named their product the "Lindy Star" sapphire.
From the 1940s through the 1950s, Union Carbide also produced a synthetic star ruby, which was also called a "Lindy."
The genuine Lindy Star cabochon was extremely popular for showy costume jewelry.
Today, these pieces are considered collector's items.
There is one other look-alike to mention: sometimes you will find what appears to be an affordable, natural, black star sapphire while shopping.
Look closely: it is more than likely a black star diopside. That specific stone will be the subject of a later gem profile!
Left: Ruby wrapped with bronze wire and hung on a garnet strand. Right: Emerald-cut Pink Sapphire (27mm x 23mm x 12mm) hung on a braided satin cord. Both wrapped by Julia McCormack.
Resources
Book Resources:
Rubies & Sapphires (Fourth Edition) by Fred Ward, ISBN-10: 9781887651103, ISBN-13: 978-1887651103
Gems and Minerals of the Bible, by Ruth V. Wright and Robert L. Chadbourne (Harper & Row Publishers, 1970)
Simon & Schuster's Guide to Gems and Precious Stones, by Curzio Cipriani and Alessandro Borelli, ISBN 0-671-60430-9
Book Resources:
Rubies & Sapphires (Fourth Edition) by Fred Ward, ISBN-10: 9781887651103, ISBN-13: 978-1887651103
Gems and Minerals of the Bible, by Ruth V. Wright and Robert L. Chadbourne (Harper & Row Publishers, 1970)
Simon & Schuster's Guide to Gems and Precious Stones, by Curzio Cipriani and Alessandro Borelli, ISBN 0-671-60430-9
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Dale Armstrong
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