Pellyite
Chemical formula: Ba<sub>2</sub>CaFe<sup>2+</sup><sub>2</sub>Si<sub>6</sub>O<sub>17</sub>
Pellyite is a rare barium, calcium, and iron silicate, forming colorless to pale yellow, tabular crystals with a vitreous luster.
Properties
- Mohs hardness
- 6
- Luster
- Vitreous
- Streak
- White
- Density
- 3.5
- Cleavage
- Good on {010} and {100}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Field identification of pellyite is practically impossible without advanced analytical methods. In a collection, it can be preliminarily recognized by its tabular crystal habit, vitreous luster, and occurrence in association with other skarn minerals. Its fluorescence under UV light is also characteristic – it glows creamy yellow under shortwave and longwave UV light. ## Distinguishing from Similar Minerals It can be confused with other colorless or pale yellow silicates found in similar environments, such as wollastonite or diopside. Differentiation requires chemical analysis (EDS/WDS) to confirm the presence of barium, calcium, and iron in appropriate proportions, as well as X-ray diffraction (XRD) to confirm the crystal structure. ## Crystal Forms Pellyite crystallizes in the orthorhombic system. It forms thin, tabular crystals with a rectangular or hexagonal outline. Crystals often occur as radial or stellate aggregates, as well as granular masses within the rock.
Geological environment
## Genesis Pellyite is a mineral of metamorphic origin. It forms in contact zones, in manganese skarns that have undergone recrystallization under the influence of regional metamorphism. Its formation is associated with specific pressure and temperature conditions and the presence of elements such as barium, calcium, and iron. ## Mineral Associations This mineral co-occurs with other minerals typical of skarns and metamorphic rocks. It is most commonly found in association with sanbornite, quartz, diopside, wollastonite, taramellite, gillespite, celsian, and hedenbergite. ## Localities The most important and type locality for pellyite is its discovery site in the Ross River area of the Yukon Territory, Canada. It is also known from a few occurrences in the USA, including Esmeralda Peak in Washington State and Mariposa County in California, where it occurs in manganese deposits.
Rarity
Very rare
For collectors
## Quality Criteria The quality of pellyite specimens is primarily assessed based on crystal habit and size. The most desirable are well-formed, sharp, tabular crystals forming aesthetic, radial aggregates. Transparency and lack of damage are also important. Specimens on a rock matrix, showing association with other rare minerals (e.g., gillespite), are more highly valued. ## Popular Localities By far the most prized and classic specimens come from the type locality in Yukon, Canada. Specimens from California, though also rare, are found on the collector's market and constitute an important addition to systematic collections.
Care and storage
## Cleaning Pellyite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid Avoid contact with acids and strong chemical agents, which can damage the mineral's surface. It should not be heated or subjected to sudden temperature changes. Due to its cleavage, it is susceptible to impacts and mechanical pressure. ## Storage Pellyite specimens, being rare and fragile, are best stored in separate, padded collector boxes to protect them from mechanical damage and dust. Avoid storing in areas with high humidity.