|Rhenium in Wolframite.|
This is basically a fine powder which is said to have been determined by neutron activation analysis to be microscopic inclusions of rhenium in wolframite grains. No reason to doubt the claim. But it is a good bit of money to pay for a powder that, honestly, looks a lot like just about any other powder.
It is described as coming from eastern Transbaikal, Russia (interestingly the tag it came with is marked "E. Transbaikal, U.S.S.R.", indicating that the sample must have been collected some time ago).
Source: Topaz Mineral Explorations
Contributor: Theodore Gray
Acquired: 20 July, 2002
Sample Group: Powders