Xonotlite, or eakleite, is a mineral of general formula Ca6Si6O17(OH)2 named by the German mineralogist Karl Friedrich August Rammelsberg in 1866. The name originates from its discovery locality, Tetela de Xonotla, Puebla, Mexico. Although it was discovered in 1866, it was first described by Taylor in 1959. It is approved by the IMA, but it is a grandfathered species, meaning the name represents a valid species til this day.
Properties
Xonotlite is an inosilicate with double dreier chains, of which several polytypes are known. The known polytypes are Ma2bc, Ma2b2c and M2a2bc. It is a calcium silicate hydrate (CSH) mineral related to the tobermorite group. It can be colorless, gray, light gray, lemon white, or pink. It is transparent with a vitreous to silky luster. It leaves a white streak. Xonotlite is rated 6.5 on the Mohs scale of hardness. It crystallizes in the monoclinic – prismatic crystal system, with typically an acicular crystal form or habit, meaning it occurs as needle-like crystals. It is massive, meaning individual crystals are hard to tell apart as they form large masses. It mainly consists of oxygen (42.52%), calcium (33.63%) and silicon (23.57%), and includes hydrogen (0.28%), the four main elements present in calcium silicate hydrates. It is a luminescent mineral; under short ultraviolet light, it has a weak gray-white fluorescence, and under long UV, it is weak white. It is not a magnetic mineral and is not radioactive.
Environment and mining
Xonotlite occurs as veins in serpentinite and contact metamorphism aureoles. Associated minerals include apophyllite, diopside, stilbite, tobermorite, clinohedrite, thaumasite, laumontite and wollastonite.
The most common impurities include iron, magnesium and carbon dioxyde (CO2) impurities. It has many type localities, the most notable one being Tetela de Ocampo, Mexico.
