krutovite

Krutovite is a cubic nickel diarsenide with a chemical composition of NiAs2 and a sulfur content of 0.02-0.34 weight percent. Krutovite is composed of nickel and arsenic with trace to minor amounts of cobalt, iron, copper, sulfur, and antimony.

==Geological occurrence== Krutovite occurs in the Geshiber vein, Svornost shaft, 8th level, in the northwest strike of Jáchymov, Czech Republic, in the Ore Mountains. The Ore Mountains are composed of two parts: the Precambrian metamorphic rocks and the Lower Paleozoic metamorphic volcano sedimentary sequence. The surrounding area lies on fault zones where many minerals develop. The Potůčky ore district where krutovite was originally found lies on the northern fault zone. Heading south is the Ore Mountains fault zone which surrounds the district of the Jáchymov. The western border is the Central Fault and the eastern border is formed by the Plavno Fault. Veins come from the major fault lines where krutovite crystallized at moderate hydrothermal temperatures. The veins can be classified into two categories: the morning veins striking along the east and west fault zone and the midnight veins striking from north to south. Krutovite comes from the midnight vein in the Svornmost mine which contains nickel ores as deep as 100 meters in the granite body. The midnight veins are known to exhibit frequent variations in their strike and dip and have an average width of 10–30 cm. In addition to nickel being mined here, silver, bismuth, and uranium were also found in the 19th century. Krutovite forms grains up to 0.1 mm in isometric or irregular form and has also been known to occur intergrowth with nickel skutterudite and sometimes with tennantite. When this occurs the intergrowth is smooth and there is no visible reaction.