White terskite associated to brown kentbrooksite from a pegmatite in Russia (Yubileinaya Pegmatite, Lovozero Massif, Kola, Russian Federation). — Photo: David Hospital · CC BY-SA 4.0
Kentbrooksite
A moderately rare eudialyte-group mineral with rare-earth substitutions and cyclic silicate groups.
Intro adapted from Wikipedia (CC BY-SA).
Kentbrooksite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na,REE)₁₅(Ca,REE)₆Mn₃Zr₃Nb(Si₂₅O₇₃)(O,OH,H₂O)₃(F,Cl)₂.
It crystallizes in the hexagonal crystal system (space group R3). It is a member of the Eudialyte structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.1; White streak; Vitreous luster; optically uniaxial.
IMA symbol Ktb, IMA status: approved, named in 1996.
Found in alkaline pegmatitic bodies cutting pulaskite.
It is found associated with Kupletskite, låvenite, catapleiite, hjortdahlite, eudialyte, alkali feldspar, nepheline, aegirine, albite.
The mineral was named to honor geologist C. Kent Brooks for significant contributions to the understanding of the Kangerdlugssuaq area as a rifted continental margin.