Yellow sapphire is also known as Oriental Topaz.In sanskrit it is called guru ratna, Pushparag, and in Persian as Yakkot.
It is basically corundum and comes in many other colors as well. The chemical composition is Aluminium Oxide.
The yellow sapphire is mainly found in Queensland and New south Wales in Australia. Even Shri lanka, East Africa also produces this type of sapphire. The sapphire has hardness of 9, specific gravity 4.00 refractive index 1.76-1.77 with a Trigonal crystal structure.
Actual yellow sapphire should feel heavy when put on one’s palm and should be spoltess. It should not have layered surface. After being rubbed with a touchstone, It should shine further. A defective or Fake piece will give sand like roughness when toughed. It can have blackish bubbles in its body. A fake will give different hues of yellow and whitish. A real sapphire would drown in a liquid whereas other fakes will ultimately came to the surface.