Another fine specimen at the Holden / Marolt Mining and Ranching Museum in Aspen, Colorado — this time, it’s a sample of barite:
Barite (a.k.a. baryte) is just the mineral form of barium sulfate. It occurs naturally in a variety of contexts, and is primarily used as a weighting agent in oil well drilling. More purified forms are also used in radiology as a contrast agent (the non-toxic if also non-tasty barium meal).