Chrysothallite is a rare thallium-bearing chloride mineral with the formula K<sub>6</sub>Cu<sub>6</sub>Tl<sup>3+</sup>Cl<sub>17</sub>(OH)<sub>4</sub>â¢H<sub>2</sub>O. Chrysothallite is unique in being only the second mineral with essential trivalent thallium, a feature shared with natural thallium(III) oxide, avicennite. Another examples of natural thallium chlorides are steropesite, Tl<sub>3</sub>BiCl<sub>6</sub>, and lafossaite, TlCl. Chrysothallite is one of numerous fumarolic minerals discovered among fumarolic sites of the Tolbachik volcano, Kamchatka, Russia The mineral is named in allusion to its colour and thallium content.
Chrysothallite contains a relative high amount of zinc admixture. Zinc is substituting for copper.
Chrysothallite may be associated with many other minerals:
The crystal structure of chrysothallite is unique. Its building elements are:
Chrysothallite is supposed to be a product of interaction of relatively high-temperature fumarolic minerals with fumarolic gas and atmospheric water, that takes place in temperatures up to .