Walstromite
Chemical formula: BaCa₂Si₃O₉
Walstromite is a rare barium calcium silicate, occurring as colorless or white, tabular crystals, prized by collectors of rare minerals.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.67
- Cleavage
- {011}, {010}, and {100}.
- Fracture
- Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Walstromite is difficult to identify visually without specialized equipment. Its key features include its occurrence in a specific geological environment (metamorphic rocks rich in barium), white color, vitreous luster, and relatively high density. It often exhibits fluorescence under ultraviolet light. However, definitive confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other white or colorless minerals found in similar parageneses, such as quartz, calcite, or other barium silicates (e.g., sanbornite). It differs from quartz by its lower hardness, and from calcite by its lack of reaction with hydrochloric acid and higher density. Identification relative to other rare barium silicates is very difficult without chemical analysis. ## Crystal Forms Walstromite crystals are usually very small, with a tabular or bladed habit. They occur as single crystals embedded in rock or form small, granular aggregates.
Geological environment
## Genesis Walstromite is a mineral of metamorphic origin. It forms as a result of contact metamorphism of barium-rich silicate rocks, such as sanbornite gneisses. It forms under conditions of high temperature and relatively low pressure, in contact with magmatic intrusions. ## Mineral Associations This mineral co-occurs with other rare barium minerals. Its typical associations include: sanbornite, quartz, celsian, diopside, fresnoite, gillespite, taramellite, and titanite. ## Localities The most important and well-known locality for walstromite, which is also its type locality, is the Big Creek area in Fresno County, California, USA. This is the main source of well-formed specimens of this mineral. It has also been reported in a few other localities worldwide, including the Wessels Mine in South Africa and in Japan.
Rarity
Very rare
For collectors
## Quality Criteria Most prized by collectors are specimens with well-formed, sharp crystals, even if they are small. Their transparency and lack of damage are important. Contrasting placement on a rock matrix, especially in association with other rare minerals (e.g., red gillespite), significantly increases the value and visual appeal of the specimen. ## Popular Localities By far the most sought-after specimens come from the type locality at Big Creek, California. Material from this location is considered the global standard for walstromite.
Care and storage
## Cleaning Walstromite 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 thoroughly dry the specimen after cleaning. ## What to Avoid As a relatively soft mineral, walstromite is susceptible to scratching. Contact with harder minerals should be avoided. It is sensitive to strong acids. It should not be heated or subjected to sudden temperature changes. ## Storage It is recommended to store walstromite specimens in separate, padded display boxes to protect them from mechanical damage and contact with other minerals. It should be protected from dust and moisture.