Corundum Species The Ruby

Hi everyone,

Today I would like to break down the types of gems and talk about each individual species.  The species I am going to discuss and learn about today is the corundum species.  The two categories that fall under this species is Ruby and Sapphire.  The name corundum is originally from India. 

Let's talk about the ruby first.  The colour is varying shades of red.  The colour streak is white.  For those of you who do not know what colour streaking is, it is when the inherent colour of the stone is determined.  This occurs when you scratch the stone on a rough porcelain plate called the streak plate.  The ruby has a Mohs hardness of 9.  It's density is between 3.97 and 4.05  The cleavage is none.  In the book Gemstones of the World by Walter Schumann cleavage is described as "Many gemstones can be split along certain flat planes, which experts call cleavage." The crystal system is (trigonal) hexagonal prisms or tables, rhombohedrons.  In Gemstones of the World this system is described as "Three of the four axes are in the same plane, are of equal length, and intersect each other at angles of 120 degrees.  The fourth axis, which is of different length, is at right angles to the others.  The difference is one of symmetry.  In the trigonal system it is three sided.  Typical crystal forms of the trigonal system are three sided prisms and pyramids, rhombohedra, and scalenohedra.  The chemical composition of the ruby is Aluminum oxide.  Its transparency is transparent to opaque.

Ruby is derived from the Latin word ruber.  The red colour of the ruby is probably what gave the ruby its name.  It was around 1800 that ruby and sapphire were recognized as belonging to the corundum species.  According to Gemstones of the World red spinel and the red garnet were also designated as ruby before 1800.  The most desirable colour for the ruby is called pigeon's blood, which is described as pure red with a hint of blue.  The substance that provides the colour for the ruby is called chromium.  When a ruby is in it rough state the stone appears dull and greasy but when it is cut the luster can rival that of the diamond.  The most common treatment done to rubies is a heat treatment to improve the colour of the gem.  Ruby is known as the hardest mineral after diamond.  Inclusions are common in rubies and do not usually affect quality.  Inclusions typically indicate natural versus synthetic stones.  To have the rare cat's-eye effect and the asterism effect( a six-rayed star) the ruby has to have included rutile needles and the cobochon cut brings out this effect.

a nice example of a star ruby

There have been some famous rubies.  The largest cuttable ruby weighed in a 400cts.  There is the Edwardes Ruby(167cts), which is in the British Museum of Natural History in London, the Rosser Reeves star ruby (138.7cts), located in the Smithsonian Institution in Washington, DC, the peace ruby (43cts) which called this because it was found in 1919 at the end of WW1.  There is also the De Long Star ruby(100cts) in the American Museum of Natural History in New York.  There are rubies in many royal insignia. For example the Bohemian St.Wenzel's crown(Prague) holds a non-faceted ruby of about 250cts.

In conclusion I would like to say that I hope everyone enjoyed reading and learning something new about the Ruby.  I had fun reading and learning new things about the ruby.  I hope to hear form everyone out there interested in this subject.  I would enjoying hearing from you what you thought about this blog or any of the others I have written about.  Please drop me line and let me know what you think.  Until next time.

The rare gem lady