Besides from diamond, another type of gemstones that is just as equally famous is Corundum. According to Moh's Scale, corundum has a hardness of 9 and a specific gravity ranges from 3.95 to 4.10. Corundum is known for its 2 famous gemstones, namely Ruby and Sapphire.
Color is the main criteria used to distinguish between ruby and sapphire. The colors of ruby include purple, purplish-red, orange-red, and bright red, where bright red ruby commands huge premium and popularity over other types of ruby. For sapphire, there are more varieties in terms of color, and usually derives its name from its color, namely Blue Sapphire, Orange Sapphire, Green Sapphire, Pink Sapphire, Yellow Sapphire, Colorless Sapphire, and Padparadscha (pink-orange).
I believe many of you have heard of unheated and heated gems. The meanings of the two terms are pretty literal, unheated gems are those gems that have not gone through any heating process, whereas heated gems are those gems that have gone through heating process to improve their qualities. So, why do we have to heat those gems? There are various answers to the question, but the two main reasons are as follow: