Good medium purple color is this SPIRIT QUARTZ Cactus Crystal. Coin for size comparison. 47.6 gram.  Crystals are priced by quality, color and size. 

Darker Purple amethyst is more highly prized and will cost more for a smaller lesser quality crystal.  Light Lavender is the most common color.

A cactus or spirit quartz is a quartz crystal that is encrusted by a second generation of smaller crystals grown on a larger crystal. These crystals were first discovered in the Magaliesberg Mountain Range in, South Africa.  

Old price on this was $50.00