Palygorskite
Drug
Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with the chemical formula (Mg, Al)₂Si₄O₁₀·4 that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Wikipedia
Color: White, grayish, yellowish, gray-green
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Lath shaped crystals, fibrous and compact masses
Crystal system: Monoclinic
Formula (repeating unit): (Mg,Al)2Si4O10(OH)·4(H2O)
Mohs scale hardness: 2 – 2.5
Optical properties: Biaxial (−)