This is a beautiful Agate sphere with Amethyst crystals.  It looks to me like the Amethyst runs entirely through this sphere because, if you look on the opposite side of this sphere, there is another area where there is a small cave with hints of crystalline structure inside.  The rest of the sphere ranges in colors from white to gray to blue.  Very nice!  This is quite an unusual look.  Agate is a member of the quartz family and, specifically, a form of Chalcedony.  Native American Indians used the different forms of Chalcedony as a Sacred Stone because of its stabilizing and balancing effect on the body, mind, emotions, and spirit.