This is an outstanding specimen of arsenopyrite and sphalerite on matrix with sharp, textbook crystals of each species. Well formed crystals of very lustrous arsenopyrite to 3.8 cm across sit mixed with splendent, black crystals of sphalerite to 3 cm. They almost totally cover a plate of matrix, and the piece is well trimmed and looks good from several angles. It look slike you took Chinese-quality arsenopyrite and glued them to Dalnegorsk-quality sphalerite. You normally do not see such superb examples of both species, together, and this is a top quality Mexican specimen for these reasons.