Julgoldite
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Julgoldite is a member of the pumpellyite mineral series, a series of minerals characterized by the chemical bonding of silica tetrahedra with alkali and transition metal cations. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: blades or prisms
Crystal system: Monoclinic; (Julgoldit-(Mg) unknown)
Optical properties: Biaxial (−)