Rats Nest Claim, Challis, Custer Co., Idaho, USA
This is a very nice specimen of heulandite. It is somewhat unusual in that it does not appear to have formed in a cavity in a basalt with associated quartz as is so often the case. Rather, this appears to have been a volcanic tuff with glassy inclusions which altered (likely due to salt water) to heulandite. Many small altered nodules are visible in the matrix, although the bulk of the heulandite has been exposed on the surface, itself once a larger glassy nodule. The large pink heulandite crystals rest upon a layer of a white tough but feathery looking layer of mordenite.