Corundum

 

Ruby and Sapphire are both gem quality corundum, which is simply aluminum oxide.  The same stuff used in abrasive emery paper.  But while emery paper will cost a couple of bucks for a pack of six or twelve sheets, ruby and sapphire are some of the most valuable gemstones in the world.

            Sapphires are available in any color but red.  Red corundum is ruby.  Blue sapphire is the most popular color, but pink, purple, yellow and green sapphires are available.  The green stones aren’t very desirable because the color is often drab and lifeless.  Pink and purple stones are popular gems and are very durable.  One of the more desirable, and expensive, sapphires is called padparascha, meaning “lotus blossom”.  This is a peach color sapphire and is sometimes found in gem bearing gravel in Sri Lanka.

            Blue sapphire is the traditional birthstone for September.  Color in blue sapphire ranges from very light blue to shades so dark they look black.  The finest “cornflower blue” color is a soft, medium blue.  Traditionally the best blues came from the Kashmir Vale in India.  If someone describes a sapphire as a “Kashmir sapphire” leave and don’t go back.  Kashmir is no longer mined and is a disputed territory on the India-Pakistan border.  Very few stones ever came from there in the first place and now it is a war zone.  Now fine blues come from Southeast Asia, Sri Lanka, China, Africa and Montana. 

            Sapphire is so commonly treated that I assume all sapphires I sell have at least been heat treated.  Heat treatment is very stable and permanent.  Some stones are diffusion treated, this is a surface color added under high heat and pressure.  I don’t sell diffusion treated rubies and sapphires.  Why?  I couldn’t sleep at night knowing I sold a clear sapphire with a thin coating of blue on it as a blue sapphire.  The coating can wear off over time and the stones can’t be polished.  Nor do I sell fracture filled stones.  A few sapphires are fracture-filled.  This uses epoxy or glass to fill inclusions and fractures.  This treatment isn’t always permanent and is easily removed accidentally with chemicals or heat used in repairs.

            Ruby should be a bright red, possibly with a hint of pink.  Some “rubies” on the market are too orange or pink to be considered ruby.  They are sold as ruby because the name sells better than pink or orange sapphire.  As a general rule if the stone looks more pink than red it is a pink sapphire.  If the stone shows any orange at all it should be considered orange sapphire.  Ruby is the traditional birthstone of July.

            Historically the finest ruby came from Burma (Myanmar).  Fine ruby is still mined in Burma, however it is now illegal to import gems from Myanmar.  Call your congressman and ask them why, Myanmar’s largest export is hardwood and we can still buy that from them, only ruby and jade suffer.  Some of the finest ruby in the world probably still comes from Burma but is smuggled across the border to Thailand.  Other sources of ruby include Laos and Viet Nam, Sri Lanka, East Africa and Madagascar, and even a small amount from North Carolina.

            Treatments for ruby are the same as for sapphire.  Ruby is also so commonly heat-treated that I assume all ruby I sell is treated.  The heat treatment improves color and reduces the appearance of common rutile inclusions.  The rutile needles in sapphire and ruby give some stones a soft “silky” appearance that is desirable as long as it doesn’t make the stone look cloudy.

            The “silk” rutile needles may be so thick to cause the phenomenon we call asterism.  These are the star rubies and sapphires.  Star corundum with good color is extremely rare, most stones look pale compared to transparent sapphire.  The exception is black star sapphire that is commonly available and popular in gentlemen’s jewelry.

            Another phenomenon sapphire is the color change sapphire.  The color usually changes from purple to blue.  The color change isn’t as pronounced as in alexandrite, but then it costs only a fraction of what alexandrite does.

            Synthetic sapphire is common and has been in production for around 100 years.  Synthetic stones are chemically the same as the genuine article but are created in a lab.  You may see these stones labeled as “created”.  I sell synthetics on request only.  Synthetics are very common in birthstone jewelry, and this is where I most often use them.  Synthetic star sapphires were developed after World War II by General Electric and were popular in the 1960’s.  They are still available and occasionally someone will request one.