Kaersutite

Chemical formula: NaCa₂(Mg₃AlTi⁴⁺)(Si₆Al₂)O₂₂O₂

Kaersutite is a dark brown or black, titanium-rich amphibole group mineral, forming prismatic crystals in igneous rocks.

## Characteristics Kaersutite is a complex silicate belonging to the amphibole group, specifically to the calcic amphibole subgroup. It is distinguished by a significant titanium content, which is responsible for its characteristic dark color. Typical specimens occur as well-formed, prismatic or columnar crystals, often with a pseudohexagonal habit. It also occurs as granular aggregates or as embedded grains within the host rock. Its color is usually dark brown to almost black. ## Physical Properties This mineral is characterized by a hardness ranging from 5 to 6 on the Mohs scale. It has a vitreous luster, and its density is approximately 3.2 g/cm³. It is typically translucent, less commonly opaque, especially in thicker fragments. It exhibits distinct cleavage on two planes, intersecting at an angle of approximately 120 degrees, which is typical for amphiboles. ## Colors and Varieties Kaersutite does not have named varieties. Its coloration is quite uniform, ranging from dark brown to black. The color variability is slight and depends mainly on the content of titanium and iron in its chemical structure. ## History and Name The mineral's name comes from its type locality – Qaarsut (formerly Kaersut) on the Nuussuaq Peninsula in Greenland. It was first described in 1884. Kaersutite is the root name mineral for the entire Kaersutite Root Name Group in mineral classification. ## Applications Kaersutite has no significant industrial applications. However, it is a mineral of scientific importance, used in petrological studies to determine the formation conditions of igneous rocks. It is also an object of interest for mineral collectors, especially well-formed crystals from classic localities.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Pale brownish-grey
Density: 3.2
Cleavage: on {110}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Kaersutite can be identified by its dark brown to black color, vitreous luster, and the characteristic amphibole cleavage at an angle of approximately 120 degrees. An important feature is its occurrence in igneous rocks such as basalts, trachytes, or syenites. The streak has a characteristic pale grayish-brown color. ## Distinguishing from Similar Minerals Kaersutite is most commonly confused with other dark amphiboles, such as hornblende, and with pyroxenes (e.g., augite). It differs from hornblende by its usually darker, more brownish color and higher titanium content (which requires chemical analysis). It differs from augite by its cleavage angle – in pyroxenes, it is approximately 90 degrees, while in amphiboles (including kaersutite), it is approximately 120 degrees. ## Crystal Forms It forms elongated, prismatic crystals, often with a hexagonal outline. It also occurs as granular, fibrous aggregates or as irregular grains embedded in the rock.

Geological environment

## Genesis Kaersutite is a typical mineral of alkaline igneous rocks, both extrusive and intrusive. It crystallizes under conditions of high temperature and low pressure. It forms in basaltic lavas, trachytes, phonolites, as well as in nepheline syenites and mantle xenoliths brought to the surface by magma. ## Mineral Associations It often co-occurs with minerals such as: sanidine, plagioclase, nepheline, augite, olivine, biotite, magnetite, and other amphiboles and pyroxenes. ## Localities Key worldwide localities include the type locality in Qaarsut, Greenland, where large crystals have been found. Other known sites include the Kola Peninsula in Russia, the Eifel region in Germany, the Mont-Saint-Hilaire massif in Canada, as well as numerous localities in the Czech Republic (e.g., within the Bohemian Massif), Italy (Vesuvius), the USA (Arizona and New Mexico states), and Australia.

Rarity

Not very common

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharply terminated crystals with a strong luster and an intense, dark brown color. The attractiveness is enhanced by the contrasting placement of crystals on a light rock matrix. Large, single crystals several centimeters in size are rare and sought after. ## Popular Localities Classic and most desirable specimens come from the type locality in Greenland. High-quality crystals are also found in the Czech Republic, especially around Lukov. Specimens from Mont-Saint-Hilaire in Canada and the Eifel region in Germany are also highly regarded by collectors.

Care and storage

## Cleaning Kaersutite specimens can be cleaned using a soft brush and distilled water. Strong detergents and ultrasonic cleaners should be avoided, as they could damage the specimen, especially along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids. Avoid sudden temperature changes and prolonged exposure to direct sunlight, although it is not considered particularly harmful. Due to its cleavage, it should be protected from impacts and falls. ## Storage Kaersutite specimens are best stored in individual, padded boxes or on stands in enclosed display cases to protect them from dust and mechanical damage. It does not require special humidity conditions.