Cumengeite
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Cumengeite, also known as cumengite, is a secondary mineral that was named after mining engineer Bernard Louis Philippe Édouard Cumenge, who found the first specimens. It is easily confused with diaboleite. Wikipedia
Crystal system: Tetragonal
Crystal class: Ditetragonal Dipyramidal; H-M Symbol: 4/mmm; (4/m 2/m 2/m)
Optical properties: Uniaxial (−)
Space group: I4/mmm
Streak: Sky-blue