Kentbrooksite from the Kangerdlugssuaq intrusion, East Greenland, a new Mn-REE-Nb-F end-member in a series within the eudialyte group: Description and crystal structure

Abstract

Kentbrooksite, ideally (Na,REE)dCa,REE)6Mn3Zr3NbSi25074F2 . 2H20, is a new mineral from the Kangerdlugssuaq intrusion, East Greenland. The mineral occurs in alkaline pegmatitic bodies cutting pu- laskite rocks and is found as anhedral to subhedral aggregates up to 2 cm. It is transparent, yellow-brown withwhite streak and vitreous luster. Hardness 5-6, brittle, uneven fracture and no cleavage. It is pyroelectric. Themineral is uniaxial negative, OJ= 1.628(2) and £ = 1.623(2), nonpleochroic. Dmcas = 3.10(4) g/cm3,Deale=