Gismondine
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Gismondine is a mineral with the chemical formula CaAl₂Si₂O₈·4. It is a zeolite or hydrated alumino-silicate. It forms colorless, bipyramidal crystals of orthorhombic symmetry.
Gismondine was named for Italian mineralogist Carlo Giuseppe Gismondi.... Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal system: Monoclinic
Formula (repeating unit): CaAl2Si2O8·4(H2O)