Koutekite

Chemical formula: Cu<sub>₅</sub>As<sub>₂</sub>

Koutekite is a rare copper arsenide, forming small, metallic grains of silvery-white or gray color, which quickly tarnish in air.

## Characteristics Koutekite is a rare mineral from the arsenide group, being a copper arsenide. It usually occurs as small, irregular grains or massive aggregates intergrown with other minerals. Freshly exposed surfaces have a silvery-white or tin-white color with a metallic luster, but in air, they quickly oxidize, becoming covered with a dull, gray or black patina. ## Physical Properties This mineral is opaque and exhibits a strong metallic luster on a fresh fracture. It is relatively soft, with a Mohs hardness of 3.5. It is also quite dense due to its high copper and arsenic content. ## Colors and Varieties The dominant color of fresh koutekite is silvery-white to tin-white. Surfaces exposed to air quickly darken to gray, and eventually to black. No varieties of this mineral are distinguished. ## History and Name Koutekite was first described in 1958 by Johan Kourim, František Novák, and Jaroslav Kvapil. The mineral is named in honor of the Czech mineralogist and geologist, Professor Jaromír Koutek (1902-1983) from Charles University in Prague, for his contributions to the study of ore deposits. The type locality is Černý Důl in the Czech Republic. ## Applications Koutekite has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare and well-defined mineral species.

Properties

Mohs hardness: 3.5
Luster: Metallic
Streak: Black
Density: 8.46
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Koutekite is identified by its metallic luster on a fresh fracture, its silvery-white color which quickly darkens, and its relatively high density. It occurs in characteristic parageneses with other copper arsenides and sulfides. ## Distinguishing from Similar Minerals It can be confused with other copper arsenides, such as algodonite or domeykite, as well as native arsenic. Differentiation requires specialized tests, most often chemical analysis (EDS) or X-ray diffraction (XRD), as the physical properties of these minerals are very similar. ## Crystal Forms Koutekite crystals are extremely rare and microscopic. It usually forms irregular grains, massive aggregates, or veinlets within the host rock. It often occurs as intergrowths with other copper arsenides.

Geological environment

## Genesis Koutekite is a hydrothermal mineral. It forms at low to medium temperatures in ore veins, typically in sulfur-poor environments rich in arsenic and copper. It occurs in calcite veins cutting metamorphosed rocks. ## Mineral Associations This mineral often co-occurs with other copper arsenides, such as algodonite, domeykite, novakite, as well as native arsenic, native bismuth, chalcocite, bornite, tennantite, lollingite, pyrite, chalcopyrite, sphalerite, and calcite. ## Localities The most important and classic koutekite localities are in the Czech Republic, in Černý Důl (type locality) and Vrančice. It is also known from the Mohawk mine in Keweenaw County, Michigan (USA), as well as from several localities in Germany (e.g., in the Harz Mountains and the Thuringian Forest) and France.

Rarity

Rare

For collectors

## Quality Criteria The quality of a koutekite specimen primarily depends on the abundance of the mineral in the sample and the presence of clearly visible, fresh surfaces with a metallic luster. Since this mineral rarely forms independent, large aggregates, specimens where koutekite is clearly visible and constitutes a significant part of the sample are most valued. Co-occurrence with other rare arsenides also increases its collector's value. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality in Černý Důl in the Czech Republic. Koutekite-rich samples from historical copper mines on the Keweenaw Peninsula in Michigan, USA, are also highly prized.

Care and storage

## Cleaning Mechanical cleaning is highly inadvisable due to its softness and tendency to oxidize. It is best to leave the specimen in the state in which it was found. Any attempts at cleaning may destroy the natural patina or the mineral itself. ## What to Avoid Avoid contact with water, chemicals, and especially moist air, which accelerates the oxidation and tarnishing process. Do not heat it or expose it to acids. Due to its arsenic content, avoid inhaling dust during any processing and wash hands after contact with the mineral. ## Storage Koutekite specimens should be stored in dry conditions, preferably in airtight, sealed boxes or containers with a desiccant. This will slow down the oxidation process and preserve, at least partially, the metallic appearance of the mineral.

Sources

IMA Mineral List (CNMNC)