Potassic-jeanlouisite

Chemical formula: K(NaCa)(Mg₄Ti₄+)Si₈O₂₂O₂

Potassic-jeanlouisite is an extremely rare amphibole group mineral, discovered in Canada, distinguished by its unique chemical composition with potassium and titanium.

## Characteristics Potassic-jeanlouisite is a titanium amphibole from the group of potassic titanium amphiboles. This mineral forms very small, prismatic crystals, typically not exceeding 1 mm in length, occurring as aggregates or individual grains within the host rock. Due to the small size of the crystals, its macroscopic features are difficult to observe without specialized equipment. ## Physical Properties Crystals exhibit strong pleochroism, changing color from dark brown to light brown depending on the observation direction. The mineral is brittle. Its Mohs hardness is approximately 6, and its density, calculated from crystallographic data, is 3.21 g/cm³. ## Colors and Varieties The observed color of the mineral is dark brown. No varieties have been distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2019 (IMA2019-039). Its name honors the Canadian mineralogist Jean-Louis Robert, in recognition of his contributions to amphibole group research. The prefix "potassic-" refers to the dominance of potassium in a specific site within the mineral's crystal structure. ## Uses Potassic-jeanlouisite has no industrial applications. Its significance is purely scientific and collector-oriented, as a unique member of the amphibole group.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: Light brown
Density: 3.21
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of potassic-jeanlouisite is impossible without advanced analytical techniques. It requires chemical analysis (e.g., using an electron microprobe) to determine its unique composition with dominant potassium and titanium, and X-ray diffraction analysis to confirm its crystal structure. Visually, in the host rock, it may be recognized as dark brown, fine, prismatic crystals. ## Distinguishing from Similar Minerals It can be confused with other dark amphiboles, such as hornblende, arfvedsonite, or other titanium amphiboles. Differentiation requires specialized laboratory studies, as visual characteristics, such as color or crystal form, are insufficient for certain identification. ## Crystal Forms The mineral forms elongated, prismatic crystals, reaching up to 1 mm in length. They occur as individual grains or small aggregates within the rock.

Geological environment

## Genesis Potassic-jeanlouisite forms under high-grade metamorphic conditions. In its type locality (Arunta Complex in Australia), it was found in granulite rocks that underwent potassic metasomatism at extremely high temperatures, exceeding 950°C. ## Mineral Associations This mineral coexists with minerals such as enstatite, quartz, plagioclase, sanidine, ilmenite, zircon, apatite, and other rare amphiboles, such as potassic-ferro-taramite. ## Localities The only confirmed and described locality for potassic-jeanlouisite is the Strangways Range in the Arunta Complex, Northern Territory, Australia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a collector's specimen primarily depends on the confirmed presence of the mineral through analysis. The abundance of crystals in the host rock and their size enhance its attractiveness, although even the largest known crystals are very small. Color contrast with surrounding minerals can also influence aesthetic value. ## Popular Localities The only source of specimens is its type locality in Australia, which makes the material extremely difficult to acquire on the collector's market.

Care and storage

## Cleaning Specimens containing this mineral should be cleaned only very carefully, using a soft brush to remove dust. Due to its brittleness and small crystal size, wet cleaning and ultrasonic cleaners should be avoided. ## What to Avoid Contact with chemicals, acids, and detergents should be avoided. The mineral should be protected from sudden temperature changes and direct, prolonged exposure to sunlight, which could potentially affect its color. ## Storage It is recommended to store specimens under stable conditions, in closed collector boxes or display cases, to protect them from dust, humidity, and mechanical damage. Due to its brittleness, avoid placing it in contact with harder minerals.

Sources

IMA Mineral List (CNMNC)