Ruby it wasnt until about the 1800s that Ruby was recgnised as belonging to the corundum family. The red colour of Ruby varies from each depsoit. The colouring agent is chromuim and the brownish tones found in some Ruby is because of iron also being present. Heat treatment of Rubies is common and now is almost standard as well as lead glass filling which is becoming more and more common as the better quaility Rubies become harder to find. Large Ruies are rarer than diamonds and as such the price reflects that. with depsoits worldwide this is one of if not the most popular gemstone pushing even that of Diamond.
About lead glass or cavity filled Ruby this treatment allows poorer colour or quaility rubies to be used in the production of jewellery. The process is simple a glass powder is placed upon the rough Ruby and then heated becuase Ruby is porous it sucks the molten glass into any cavitys or cracks thus sealing them and enables them to be used as gem quaility stones and also allows the price to be that much lower than an un heated/treated gem thta the prices falls within anybodys budget.
Rubies in the past where belived to ward off misfortune and illness.
It has a mohls hardness scale of 9 and a refractive index of 1.762-1.778.