Topaz, is a silicate mineral made of aluminum and fluorine.  It is used as a gemstone in jewelry and other adornments.  Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow-orange, or in the case of this particular Topaz, black. This particular Topaz will not bleach in the sun, the impuriteis that make it black are contained within the stone and are not sensitive to UV.  
 
Topaz is one of the hardest naturally occurring minerals with a hardness of 8, just behind Corundum (ruby) at 9, and Diamond at 10.