Ludlamite
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Ludlamite is a rare phosphate mineral with chemical formula (Fe, Mn, Mg)₃(PO₄)₂·4H₂O. It was first described in 1877 for an occurrence in Wheal Jane mine in Cornwall, England and named for English mineralogist Henry Ludlam. Wikipedia
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Tabular crystals; massive, granular
Crystal system: Monoclinic
Formula (repeating unit): (Fe,Mn,Mg)3(PO4)2·4H2O