Nice Untreated Natural Yellow sapphire gemstone.

Sapphire

    Color: any color
    Hardness: 9
    Refractive index: 1.76 - 1.78
    Density: 3.99 - 4.00
    Chemical composition: Al2O3
    Crystal structure: hexagonal
    Origins: Sri Lanka, India, Madagascar, Kenya, Tanzania, Thailand, Cambodia, China, Australia, USA.

Sapphires are a variety of corundum, existing in almost all colors. A sapphire's color is the main factor for price estimation. Heat treatment is usually applied to improve their color and reduce small inclusions.