Mineral name:  Gypsum variety Satin Spar Chemical formula:  CaSO4.2H2O Location:  Brewster County, Texas Crystal system and class:  Monoclinic  2/m Genesis:  Satin spar gypsum typically crystallizes in hydrothermal veins, or through the recrystallization of massive gypsum deposits formed through the precipitation of evaporating salt water.  The curved satin spar crystals shown above precipitated from calcium sulfate-bearing groundwater in solution cavities. Width x length of field of view in cm:  8  x 11 Specimen number:  E