Semseyite
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Semseyite is a rarely occurring sulfosalt mineral and is part of the class of lead antimony sulfides. It crystallizes in the monoclinic system with the chemical composition Pb₉Sb₈S₂₁. The mineral forms dark gray to black aggregates. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Tabular, elongated prismatic crystals, commonly twisted; rosettelike groups
Crystal system: Monoclinic