THE MINERAL THOMSENOLITE

Chemistry: NaCaAlF6 - H2O, Hydrated Sodium Calcium Aluminum Fluoride.
Class: Halides
Uses: As mineral specimens.
Specimens

Thomsenolite is a rare and unusual halide mineral. Chemically it is one of the most complicated halides being composed of the positive one charged (+1) sodium, the positive two charged (+2) calcium and the positive three charged (+3) aluminum. These six positive charges are countered by the six negative one charged (-1) fluorines. The symmetry of thomsenolite is also unusual in that it is monoclinic, not unusual for minerals in general as many minerals are monoclinic, but unusual for halide minerals.

Thomsenolite forms from the alteration of cryolite, another unusual halide mineral which by no small chance is associated with thomsenolite. Thomsenolite also is found with the mineral pachnolite which has the same chemistry as Thomsenolite but has a slightly different structure. The better cleavage and softness of thomsenolite and its more obvious monoclinic crystal habit serve to distinguish it from pachnolite. Both minerals are found as druses lining the pockets of the very unique pegmatitic rocks at Ivigtut, Greenland.

PHYSICAL CHARACTERISTICS:

Color is colorless or white.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic.
Crystal Habits include druses of prismatic crystals with a distinctly monoclinic slant. Also pseudo-cubic crystals are common.
Cleavage is perfect.
Fracture is conchoidal.
Hardness is 2
Specific Gravity is 2.9 (average).
Streak is white.
Associated Minerals include pachnolite, cryolite, ralstonite and limonite.
Notable Occurrences are limited to Ivigtut, Greenland and other southwestern Greenland localities.
Best Field Indicators are crystal habit, softness, associations, locality and good cleavage.