THE MINERAL PACHNOLITE

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

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Pachnolite 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 pachnolite is also unusual in that it is monoclinic, not unusual for minerals in general as many minerals are monoclinic, but unusual for halide minerals.

Pachnolite forms from the alteration of cryolite, another unusual halide mineral which by no small chance is associated with pachnolite. Pachnolite also is found with the mineral thomsenolite which has the same chemistry as pachnolite 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, white or stained yellow to brown by limonite.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent.
• Crystal System: Monoclinic.
• Crystal Habits include prismatic crystals with steep pyramidal terminations. Also pseudo-orthorhombic twinned prismatic crystals are common but tabular crystals are rare.
• Cleavage is very indistinct.
• Fracture is conchoidal.
• Hardness is 3
• Specific Gravity is 2.98 (average).
• Streak is white.
• Associated Minerals include thomsenolite, cryolite, ralstonite and limonite.
• Notable Occurrences are limited to Ivigtut, Greenland.
• Best Field Indicators are crystal habit, associations, locality and lack of good cleavage.