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.
Color is colorless, white or stained yellow to brown by limonite.
Luster is vitreous. Crystals are transparent to translucent. 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.