Coral

Chemical Formula	Mostly calcium carbonate
Color	White, Red, Orange, Pink, Gray, Black
Hardness	3 - 4
Crystal System	Amorphous
Refractive Index	1.48 - 1.65
SG	2.6 - 2.7
Transparency	Translucent to opaque
Double Refraction	-.172
Luster	Vitreous, waxy
Cleavage	None