Carlhintzeite
Chemical formula: Ca<sub>2</sub>AlF<sub>7</sub>·H<sub>2</sub>O
Carlhintzeite is a very rare, hydrated calcium aluminum fluoride, forming colorless or white, tabular crystals in pegmatite vugs.
Description
## Characteristics Carlhintzeite is a rare secondary mineral, valued in collecting circles. It typically forms small, colorless or white crystals with a tabular or short-prismatic habit. It occurs as small druses and crystal aggregates lining cavities in the host rock. Crystals often arrange into subparallel or radial aggregates. The mineral's luster is vitreous, and its transparency ranges from transparent to translucent. ## Physical Properties It is a relatively soft mineral, with a hardness of about 2.5 on the Mohs scale, meaning it can be scratched with a fingernail. It has a density of 2.81 g/cm³, typical for fluoride minerals. It is characterized by perfect cleavage in one direction, which makes it brittle and susceptible to mechanical damage. ## Colors and Varieties Carlhintzeite occurs almost exclusively in colorless or white forms. There are no distinct color varieties or commercial names for it. ## History and Name The mineral was first described in 1981 by A. Mücke. Its name honors Carl Hintze (1851–1916), a prominent German mineralogist and crystallographer, author of the fundamental work "Handbuch der Mineralogie." ## Applications Due to its extreme rarity and small crystal size, carlhintzeite has no industrial applications. It is solely an object of scientific and collecting interest.
Diagnostic features
## Identification Identifying carlhintzeite is difficult and usually requires advanced analytical methods, such as X-ray diffraction (XRD). Preliminary identification is based on its specific occurrence environment (vugs in pegmatites), associated minerals (fluorite, creedite), tabular crystal habit, softness, and perfect cleavage. ## Distinguishing from Similar Minerals Carlhintzeite can be confused with other colorless or white secondary minerals found in similar environments, such as creedite, gearksutite, or ralstonite. Creedite typically forms radial aggregates of acicular crystals and crystallizes in the monoclinic system. Gearksutite often has an earthy or chalky appearance. Definitive differentiation requires laboratory analysis. ## Crystal Forms Crystals are small, tabular, flattened parallel to the cleavage plane, or short-prismatic. They most often form druses, crusts, and small, rosette-like or subparallel aggregates in rock cavities.
Geological environment
## Genesis Carlhintzeite is a secondary mineral, formed under low-temperature hydrothermal processes. It forms in vugs and fractures of granitic pegmatites, likely as a result of the alteration of primary fluorine-bearing minerals. ## Mineral Associations This mineral occurs in association with other fluorides and secondary minerals. It most commonly co-occurs with fluorite, creedite, gearksutite, as well as quartz and microcline feldspar. ## Localities The only known and confirmed locality for collectible carlhintzeite is its type locality – the Hagendorf-Süd pegmatite in Waidhaus, Upper Palatinate, Bavaria (Germany).
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly prized carlhintzeite specimens are those with well-formed, sharp, and transparent crystals, forming aesthetic druses on a contrasting matrix, for example, on purple fluorite. Crystal size is a key factor – specimens with crystals exceeding a few millimeters are exceptionally rare and sought after. The aesthetics of the overall composition and the absence of damage are also important. ## Popular Localities All collectible carlhintzeite specimens originate from a single location in the world: the famous Hagendorf-Süd pegmatite in Germany. This is a classic locality for many rare phosphate and fluoride minerals, and specimens from there are highly valued by specialists.
Care and storage
## Cleaning Carlhintzeite specimens are very delicate and should be handled with extreme care. For dust removal, a soft brush is best. If necessary, the specimen can be very carefully rinsed in distilled water and then immediately dried. Ultrasonic cleaners should be avoided, as they could damage the fragile crystals. ## What to Avoid The mineral is soft and has perfect cleavage, making it very sensitive to impact, scratches, and vibrations. As a hydrated mineral, it can be damaged (dehydrated) by high temperatures. Contact with acids and strong chemicals should be avoided. ## Storage Collectible carlhintzeite specimens should be stored separately in a padded box to prevent contact with harder minerals. They should be protected from dust, direct sunlight, and sudden temperature changes.