Gjerdingenite-Ca

Chemical formula: K₂Ca(Nb₅+,Ti₄+)₄(Si₄O₁₂)₂(O,OH)₄·₆H₂O

Gjerdingenite-Ca is a very rare mineral from the cyclosilicate group, found as tiny, radial aggregates in syenite pegmatites.

## Characteristics Gjerdingenite-Ca is a mineral from the gjerdingenite group, belonging to the cyclosilicates. It forms very small, acicular or bladed crystals, which usually occur as radial or spherulitic aggregates. Individual crystals rarely exceed 1 mm in length. Due to its small size, its visual features are difficult to observe without magnification. ## Physical Properties The mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a white streak and a vitreous luster. It is brittle, and its calculated density is approximately 2.98 g/cm³. Crystals are transparent to translucent. ## Colors and Varieties Gjerdingenite-Ca occurs in shades from colorless and white to pale yellow or light brown. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition, indicating the dominance of calcium (Ca) in its structure, and alludes to its kinship with other minerals from the gjerdingenite group. This group, in turn, took its name from the type locality – Gjerdingen in Norway. Gjerdingenite-Ca was approved as a new mineral by the International Mineralogical Association (IMA) in 2005 (IMA2005-032).

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.98
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of Gjerdingenite-Ca is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS/WDS) combined with X-ray diffraction (XRD). Visually, at the occurrence site, it can be suspected based on characteristic, small, radial aggregates of a light color within syenite pegmatites. ## Distinguishing from Similar Minerals It can be confused with other minerals from the gjerdingenite group (e.g., Gjerdingenite-Fe, Gjerdingenite-Mn, Gjerdingenite-Na) and other rare cyclosilicates occurring in similar environments, such as eudialyte or astrophyllite. Definitive differentiation requires specialized laboratory tests. ## Crystal Forms It forms acicular or bladed crystals, elongated along the [010] axis and flattened parallel to {001}. They most often occur in the form of radial, stellate, or spherulitic aggregates.

Geological environment

## Genesis Gjerdingenite-Ca is a mineral of magmatic origin, crystallizing in the late stages of syenite pegmatite evolution. It forms under low-temperature conditions in rock cavities and fractures. ## Mineral Associations It co-occurs with minerals such as microcline, albite, aegirine, quartz, natrolite, eudialyte, catapleiite, elpidite, lorenzenite, astrophyllite, fluorite, and minerals from the gjerdingenite group. ## Localities This is an extremely rare mineral, known from only a few locations worldwide. The most important of these are: - Type locality: Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. - Other occurrences: Khibiny Massif and Lovozero Massif on the Kola Peninsula in Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, its collector value depends primarily on the quality and completeness of the radial aggregates. The most prized specimens are those where the aggregates are well-formed, undamaged, and set on an aesthetic rock matrix. The size of the aggregates, although always small, is also important – larger and more distinct clusters are more desirable. Due to its rarity, every well-documented specimen has high scientific and collector value.

Care and storage

## Cleaning Due to the extreme rarity and fragility of specimens, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid ultrasonic cleaners, steam cleaners, acids, and all chemical solvents. The mineral is brittle and sensitive to shocks and temperature changes. ## Storage Specimens should be stored exclusively in specialized "micromount" boxes, protecting them from mechanical damage, dust, and moisture. Avoid exposure to direct sunlight.

Sources

IMA Mineral List (CNMNC)