Tyrrellite is a

selenide mineral Selenide minerals are those minerals that have the selenide anion as a main component. Selenides are similar to sulfides and often grouped with them. Examples include: * achavalite * athabascaite * clausthalite * ferroselite * penroseite ...

that has a chemical formula of . It has been found in the Goldfields District in northern

Saskatchewan Saskatchewan ( ; ) is a province in western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on the south by the U.S. states of Montana and North Dak ...

, as well as in the Petrovice deposit,

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

. It is named after the Canadian geologist Joseph Burr Tyrrell. Joseph Tyrrell was one of the first geologists from the Geological Survey of Canada to do research in the Goldfields District.Harris, D.C. (1970) New Data on Tyrrellite. The Canadian Mineralogist, 10, 731-735.

Crystallography

Tyrrellite is isometric, meaning that crystallographically, it has three axes of equal length perpendicular to one another. It belongs to the space group, Fd3m. Because tyrrellite is isometric, it is also isotropic. Isotropic minerals are defined as follows: when light passes through an isometric mineral, the light moves in all directions with equal velocity. In contrast, for anisotropic minerals, the velocity of light passing through the mineral varies with crystallographic direction.Klein, C., Dutrow, B. (2007) The 23rd edition of the Manual of Mineral Science. John Wiley Publishers, p. 290 Tyrrellite displays a light bronze color when viewed in plane polarized light. Because tyrrellite is isotropic, the light bronze color will remain constant as the mineral is rotated and viewed from different crystallographic angles. When viewed under cross polarized light, tyrrellite displays total extinction, a characteristic trait of isotropic minerals.

Discovery and occurrence

It was first described in 1953 for an occurrence in the Goldfields District, Saskatchewan, while the second occurrence was reported in Petrovice deposit, Czech Republic. In general, tyrrellite is veined, embayed and replaced by

umangite Umangite is a copper selenide mineral, Cu3 Se2, discovered in 1891. It occurs only in small grains or fine granular aggregates with other copper minerals of the sulfide group. It has a hardness of 3. It is blue-black to red-violet in color with ...

, a primary mineral of deposits in which tyrrellite is found. The relative scarcity and unique occurrences of tyrrellite can give geologists considerable insight into the circumstances under which the parent rock formed.

References

{{Reflist Copper minerals Cobalt minerals Nickel minerals Selenide minerals Thiospinel group Cubic minerals Minerals in space group 227