Simmonsite

Simmonsite contains no observable euhedral crystals but it does have complex polysynthetic twinning. Its color is pale buff to cream in the hadn specimens accompanied by a white streak and has a greasy appearance. It exhibits a hardness of 2.5-3 on the Mohs hardness scale. There is no apparent cleavage, a subconchoidal fracture, no parting, and is not brittle. The measured density is 3.05(2) g/cm.

Simmonsite, cryolite and cryolithionite form together as part of the alumino-fluoride aassemblage in a late stage breccia pipe structure that cross the Zapot amazonite-topaz-zinnwaldite pegmatite located in the described location above in Nevada. This assemblage occurs with around a third of each of theses phases. The three phases form an intergrowth of anhedral to subhedral grains that can be micrometers to approximately two or three hundred micrometers in size. The main anhydrous alumino-fluorides results in size almost 20cm or more across and weight more than 1kg. Another assemblage of alumino-fluorides exist, some that contain water or hydroxyl, pachnolite, weberite, thomsenollite, prosopite, ralstonite, as well as a second generation of cryolithionite.