Formula: Ca2(Fe,Mg,Mn)Al2(SiO4)(Si2O7)(OH)2.H2O
Origin of name: for R. Pumpelly, American geologist
Crystal system: monoclinic
Crystal class: 2/m
Twinning:
Unit cell:
Colour: blue-green, green, brown
Diaphaneity: translucent
Luster: vitreous
Habit: crystals fibrous or narrow plates, stellate clusters, dense mats
Hardness: 6
Specific gravity: 3.18 to 3.23
Cleavage: 2; {100} and {001} distinct
Tenacity:
Streak:
Synonyms/varieties:
Comments: four distinct species with the extensions -(Fe2+), -(Fe3+), -(Mg) and -(Mn2+) indicating the predominant cation in the formula, series between the individual species and julgoldite
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