Best of species crystals for fettelite! Fettelite is an extremely rare silver-mercury-arsenic sulfide (sulfosalt) and is found at only four total worldwide localities. These pieces represent those from which the crystal structure was determined by Frank Keutsch and others as published in the American Mineralogist in 2009 and these two pieces are from his personal collection. This is a display specimen with rich crystals of scarlet to wine-red crystals of fettelite to 2mm on bright metallic proustite and as granular, wine-red aggregates in proustite. Comes with Keutsch label noting that this specimen was in the same lot used to determine the structure type.