A superb twinned crystal of Ferberite from the Tasna mine in southern Bolivia. The piece was mined at the beginning of 2008, which is encouraging as very little in the way of Ferberites have come from this mine in recent years. This piece features the classic, "butterfly" twinning of Ferberite along the (100) face. It is a good quality, sharp, lustrous, aesthetic jet-black twinned crystal with associated botryoidal Marcasite. It has an attractive thick blocky form, and is a wonderful large thumbnail / toenail size specimen.