Vuagnatite
Chemical formula: CaAlSiO<sub>4</sub>(OH)
A rare calcium and aluminum silicate, forming small, vitreous crystals of pale blue, greenish, or violet color.
Properties
- Mohs hardness
- 6-6.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.43
- Cleavage
- Good on {110} and {011}
- Fracture
- Conchoidal to Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Helpful features for identifying vuagnatite include its relatively high hardness (6-6.5), vitreous luster, prismatic crystal habit, and characteristic pastel colors. However, the environment of occurrence is crucial – its presence in rodingites and serpentinites is a strong diagnostic indicator. ## Distinguishing from Similar Minerals Vuagnatite can be confused with minerals occurring in similar parageneses, such as prehnite, vesuvianite, or hydrogrossular. Prehnite is slightly softer (6-6.5) and crystallizes in the orthorhombic system, but often forms botryoidal or fan-shaped aggregates. Vesuvianite is harder (approx. 7) and crystallizes in the tetragonal system. The definitive distinction of these minerals often requires advanced studies, e.g., by X-ray diffraction (XRD) method. ## Crystal Forms Vuagnatite crystals have a prismatic habit, ranging from short and stout to elongated, acicular. The prism faces are often longitudinally striated. It also occurs as granular, fibrous, or radial aggregates embedded in the rock.
Geological environment
## Genesis Vuagnatite is a product of low-temperature metamorphism or hydrothermal processes. It forms in a specific geological environment, within rodingites – rocks formed by calcium metasomatism of gabbros and other mafic rocks within serpentinites and ophiolite complexes. ## Mineral Associations This mineral co-occurs with other minerals typical of rodingites and serpentinites, such as prehnite, hydrogrossular, vesuvianite, diopside, chlorite, and zoisite. ## Localities The most important vuagnatite localities worldwide include the type locality in the Poschiavo Valley in Switzerland; the Mersin area in Turkey; Red Mountain in California and Whatcom County in Washington State (USA); Okayama Prefecture in Japan; and ophiolites in Oman. It is a rare mineral in all these locations.
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, sharp, and transparent crystals of a distinct, pale blue or greenish color. Rich groups of crystals on a rock matrix are also highly prized, especially in association with other rare minerals. Crystal size is a key factor – any specimen with crystals exceeding a few millimeters is considered exceptional. ## Popular Localities Specimens from localities in Turkey (Mersin) and California (Red Mountain) are considered the best in terms of crystal quality and size. Specimens from Switzerland, although often small, are historically significant as material from the type locality.
Care and storage
## Cleaning Vuagnatite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to the presence of cleavage planes, the use of ultrasonic cleaners, which could cause crystal fracturing, is not recommended. ## What to Avoid This mineral is sensitive to strong acids. Avoid sudden temperature changes and prolonged exposure to direct sunlight, although its sensitivity to this factor is not fully documented. ## Storage It is recommended to store specimens in separate, padded boxes to protect them from mechanical damage, scratching by harder minerals, and dust accumulation. They are best kept in stable room conditions.