Dana classification 64.1.2.1 | Crystal system Trigonal | |
Category Silicate mineral, Cyclosilicate Formula(repeating unit) (Na,REE)15(Ca,REE)6Mn3Zr3NbSi25O74F2·2H2O (original form) Strunz classification 9.CO.10 (10 ed)8/E.23-20 (8 ed) Crystal class Ditrigonal pyramidal (3m)H-M symbol: (3m) | ||
Kentbrooksite is a moderately rare mineral of the eudialyte group, with formula (Na,REE)15(Ca,REE)6Mn3Zr3NbSi[(Si9O27)2(Si3O9)2O2]F2·2H2O. This extended formula shows the presence of cyclic silicate groups and dominance of Si at the M4 site, according to the nomenclature of the eudialyte group. The characteristic features of kentbrooksite, that make it different from eudialyte are: (1) dominancy of fluorine (the only currently known example among the whole group), (2) dominancy of manganese, and (3) dominancy of niobium. Trace hafnium and magnesium are also reported. Kentbrooksite is relatively common when compared to most other species of the group.
Occurrence
Kentbrooksite was found in alkaline pegmatites within pulaskites of the Kangerdlugssuaq intrusion in East Greenland.