Krutovite
Chemical formula: NiAs<sub>2</sub>
Krutovite is a rare nickel arsenide with a metallic luster, occurring as small, cubic crystals and granular aggregates.
Properties
- Mohs hardness
- 5.5
- Luster
- Metallic
- Streak
- Black
- Density
- 7.85
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Cubic
Diagnostic features
## Identification Krutovite is identified by its cubic crystal form, tin-white color, metallic luster, and high density. Its occurrence in association with other nickel and cobalt arsenides in hydrothermal veins is key. Final identification requires advanced analytical methods, such as EDS/WDS analysis, due to its similarity to many other arsenides. ## Distinguishing from Similar Minerals Krutovite is visually almost impossible to distinguish from skutterudite (Co,Ni)As₃ and chloanthite (NiAs₃) without chemical analysis. It differs from them in chemical composition (it is a diarsenide, not a triarsenide) and crystal structure. It can also be confused with gersdorffite (NiAsS), from which it differs by the absence of sulfur in its composition. ## Crystal Forms Krutovite crystallizes in the isometric system, forming small, well-formed cubes. It also occurs as granular aggregates and irregular intergrowths with other minerals.
Geological environment
## Genesis Krutovite is a mineral of hydrothermal origin. It forms in ore veins with nickel-cobalt-arsenic mineralization, cutting metamorphic rocks such as mica schists and amphibolites. It forms under medium to low-temperature conditions. ## Mineral Associations This mineral often co-occurs with other arsenides, such as skutterudite, safflorite, rammelsbergite, niccolite, as well as gersdorffite, maucherite, native bismuth, native silver, uraninite, and calcite, which often constitutes the main vein mineral. ## Localities The most important and classic localities for krutovite are the deposits in the Ore Mountains (Erzgebirge), on the border of the Czech Republic and Germany. On the Czech side, this is Potůčky (Breitenbach), and on the German side, the Anna mine in Alsdorf and the Schneeberg and Annaberg areas. It is also known from the Ait Ahmane mine in Morocco.
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and lustrous microcrystals of krutovite, clearly visible on a contrasting matrix, most often white calcite. Rich granular aggregates are also highly prized. Due to the microscopic size of the crystals, their quality and the possibility of observation under magnification are crucial. ## Popular Localities Specimens of greatest scientific and collecting importance come from the type localities in the Czech and German Ore Mountains (Potůčky, Schneeberg). In recent years, interesting specimens from the Ait Ahmane mine in Morocco have also appeared on the market, providing well-formed microcrystals.
Care and storage
## Cleaning Krutovite specimens, especially microminerals, should be cleaned with utmost care. The safest method is to use compressed air to remove dust. For heavier soiling, a soft brush and pure isopropyl alcohol can be used, avoiding soaking the entire specimen, especially if it is mounted on a sensitive matrix. ## What to Avoid Contact with acids and other aggressive chemicals, which can quickly damage the mineral's surface, must be strictly avoided. Krutovite is an arsenide, so inhaling dust generated during any processing should be avoided. It should not be heated or cleaned in ultrasonic cleaners. ## Storage Krutovite specimens are best stored in closed, stable containers (e.g., micromount type) to protect them from dust, mechanical damage, and moisture. Due to its arsenic content, it is recommended to store it away from food and to wash hands after handling the mineral.