Tschermakite

Chemical formula: &#₉₇₂₃;Ca₂(Mg₃Al₂)Si₆Al₂O₂₂(OH)₂

Tschermakite is a mineral from the amphibole group, a calcium, magnesium, and aluminum aluminosilicate, forming prismatic crystals ranging in color from green to black.

## Characteristics Tschermakite is a mineral belonging to the amphibole group, specifically to the calcic amphibole subgroup. Chemically, it is a complex calcium, magnesium, and aluminum aluminosilicate. It forms elongated, prismatic crystals, often terminated by steep faces. It also occurs as granular, fibrous aggregates, or as embedded grains within rock. Its appearance is typical of many amphiboles, with a characteristic cross-section of the crystals. ## Physical Properties The hardness of tschermakite on the Mohs scale is 5-6, placing it in the same category as feldspars. It has a density of approximately 3.15 g/cm³. The luster is typically vitreous, and the mineral can be transparent, though it is more often translucent to opaque in thicker fragments. It exhibits distinct cleavage in two directions, which is a characteristic feature of amphiboles. ## Colors and Varieties This mineral takes on various shades of green – from medium saturated, through dark green, to green bordering on black. Black specimens are also found, and more rarely, brown ones. No named color varieties or commercial varieties are distinguished. ## History and Name The name "tschermakite" was given in honor of Gustav Tschermak von Seysenegg (1836-1927), an Austrian mineralogist and petrographer, professor at the University of Vienna. Tschermak made significant contributions to the study of meteorites and rock-forming minerals, including pyroxenes and amphiboles. The mineral was formally described and named in 1945.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: Pale grey-green
Density: 3.15
Cleavage: on {110}
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Tschermakite is identified by its prismatic habit, dark green to black color, and vitreous luster. A key diagnostic feature, common to amphiboles, is the angle between cleavage planes of approximately 124° and 56°, visible in the cross-section of the crystals. The streak has a characteristic pale grayish-green color. ## Distinguishing from Similar Minerals Tschermakite is difficult to distinguish from other dark amphiboles (e.g., hornblende, pargasite) and pyroxenes (e.g., augite) without advanced studies (chemical analysis, X-ray diffraction). It is primarily distinguished from pyroxenes by its cleavage angle – for pyroxenes, it is close to 90°. Distinguishing it from other amphiboles within the same series requires specialized analysis. ## Crystal Forms Crystals are most often elongated, columnar, or prismatic. It also occurs in granular, fibrous, radial aggregates, or as anhedral grains in the host rock.

Geological environment

## Genesis Tschermakite is a metamorphic mineral. It forms under conditions of medium to high-grade regional metamorphism, especially in calcium- and aluminum-rich rocks. It is a typical component of amphibolites, amphibole gneisses, and some eclogites and granulites. It can also crystallize in some igneous rocks. ## Mineral Associations It co-occurs with other metamorphic minerals such as plagioclase (especially anorthite), garnets (almandine, pyrope), epidote, zoisite, kyanite, sillimanite, as well as other amphiboles and pyroxenes (omphacite, diopside). ## Localities Significant and well-documented occurrences of tschermakite are known from several places worldwide. It occurs in the Saualpe metamorphic complex in Carinthia (Austria), from which classic specimens originate. It is also found in Sweden (near Falun), Norway, Greenland (Fiskenæsset region), USA (New York and California states), and Canada.

Rarity

Not very common

For collectors

## Quality Criteria For collectors, the most valuable specimens are those with well-formed, sharply terminated crystals with a distinct, prismatic habit. Crystals with intense green color and good luster are prized. Specimens with contrasting matrix rock or in association with other minerals, such as garnets, enhance their attractiveness. Crystal size is also important, although large, well-formed crystals are rare. ## Popular Localities The most classic and highly valued tschermakite specimens by collectors come from Austria, especially the Carinthia region. Specimens from Greenland are also sought after due to their scientific significance and often good quality.

Care and storage

## Cleaning Tschermakite specimens can be cleaned with a soft brush under running water. For heavier soiling, distilled water and a mild detergent can be used, followed by thorough rinsing. Ultrasonic cleaners should be avoided, as they can damage the specimen along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids, which can etch it. Avoid sudden temperature changes and prolonged exposure to direct sunlight, although it is not particularly harmful. Due to its hardness (5-6), it is susceptible to scratching by harder minerals, such as quartz. ## Storage Collector's specimens of tschermakite are best stored in individual boxes or on a soft surface to prevent scratches and chipping. Protect from dust and contact with chemicals. It does not require special humidity conditions.