was identified by X-ray diffraction and SEM-EDS analysis as part of an intimate admixture of the late-stage alumino-fluoride assemblage.
Recently doyleite was also found in contact-zone cavities as white, powdery aggregates admixed with gibbsite and associated with thomsenolite and cryolite.
In a very rare and unusual mineral assemblage, gibbsite was found as cavity fillings in the contact zone in close association with cryolite, thomsenolite and doyleite.
Thomsenolite NaCaAl[F.sub.6][multiplied by][H.sub.2]O
Thomsenolite is a relatively rare mineral, known most notably from Ivigtut, Greenland (type locality) and also from lesser-known occurrences in Colorado, Utah, Norway, Ukraine, Russia and Nigeria.
Thomsenolite was found in a very unusual mineral assemblage in the contact zone of the sill, consisting of leached cryolite and cellular masses of thomsenolite, gibbsite and doyleite.
It is also found associated with thomsenolite, topaz, phenakite, cryolithionite and fluorite (Palache et al., 1951) in a cryolite pegmatite at Miass in the Ural Mountains of Russia.
Peter's Dome, El Paso County, Colorado, where microcrystalline aggregates are found sparingly with pachnolite, cryolite, prosopite, thomsenolite and gearksutite in aluminum fluoride pegmatites.
Thomsenolite and pachnolite are dimorphous forms which generally occur together in cryolite solution cavities.
Pachnolite is biaxial positive with 2V = 76[degrees], and thomsenolite is biaxial negative with 2V = 50[degrees].
Thomsenolite is clear, colorless, and characteristically forms aggregates of blocky crystals in parallel orientation.