  Brookite.  
I actually bought this crystal by mistake: I was going through mindat.org looking up the name of every single mineral that contains thorium, then searching on eBay to see if I could buy one of them.  (I needed more pictures of thorium crystals to use for the short-lived radioactive elements that appear in the thorium decay chain.)  For some reason I got confused and bough this one too: It's titanium dioxide with no hint of anything radioactive.  But it's pretty just the same! 
This is officially described as Brookite and smoky quartz from Magnet Cove. 
Source: eBay seller crystaldigger 
Contributor: Theodore Gray 
Acquired: 20 September, 2005 
Price: $29 
Size: 2.2" 
Composition: TiO2
 |  
  |  
 |  
  |