Rubies are considered one of the most expensive and valued gems in the world. They are in the highest class of precious stones along with diamond and sapphire. Rubies have a high hardness and toughness which make them a good jewelry stone and are only found in certain places of the world. Typically rubies are a deep red but depending on the content of other impurities in them, the color can change. This of course begs the questions of how are these valued gems formed and what are their composition.
Formation of rubies
The majority of the deposits of ruby in the world are formed in one specific area. This area is a stretch of marble 1,800 miles long in the southern part of the Asian contentment. The actual formation of rubies took place beneath the surface and was the result of the tectonic plates of India and Asia smashing into each other and forming the Himalayas.
Approximately 50 million years ago, their existed an ocean which was known as the Tethys Sea that was between the subcontinents of India and Asia. The bed of the sea had numerous deposits of limestone and other calcium carbonates. The limestone contained many impurities such as aluminum, chromium, oxygen, and silica which are the proper ingredients to make rubies.
As the two subcontinents constricted the sea and reached each other, the limestone on the ocean was pushed under the earth’s surface where it was exposed to great amounts of heat and pressure. These conditions and the presence of the right constituents were exactly what was needed to form marble. However marble is not ruby but this process was not yet complete. Molten granite mixed with the marble and in a process known as metasomatism, the silica present in the marble was removed and replaced with aluminum. This process created the group of minerals called corundums, of which ruby is a member. Over the course of the next 40 or more million years, the Himalayas were created by the pushing subcontinents and the ruby deposits were brought to the surface and exposed due to erosion and weathering.
Chemical Composition
Rubies, as stated before, are part of a group of minerals known as corundums. This grouping of minerals is composed almost entirely of Alumina (Al2O3) with some other impurities. Because of how they were formed, the corundums have hardened to an incredible degree which is only one unit of hardness lower than diamonds and makes them some of the hardest substances on earth.
Whereas most corundums are gray or white and made of dull colors, a small amount of them are more transparent and have a higher purity and color. Rubies fall into this category and are primarily a red color but can also appear as a reddish-brown, purplish-red, orangish-red, or pinkish-red depending on the amount of chromium impurity in the Ruby. The chromium replaces the Aluminum and forms Chromium (III) oxide (Cr2O3). Rubies also have a property known as pleochroism which means that depending on which direction the light hits them and which angle they are viewed from, the color can change.
Historically, Asia has been the primary producer of rubies as it comprised the largest deposits of rubies, specifically from countries like Thailand, Burma, and Sri Lanka. However, smaller deposits of rubies have been found in the United States, Australia, and Africa. The best quality rubies are typically from Burma and sometimes these rubies fluoresce in sunlight meaning that they will glow.
Synthetic Ruby
Since around the 1900s, people have been able to make synthetic rubies.. The initial method was flame fusion processes that simulate what happened when they were formed beneath the earth’s surface. These synthetic gems could be discerned from real ones but better processes since then have also lead to difficulty telling real ruby apart from the synthetic ruby.
