Collinsite
Chemical formula: Ca<sub>2</sub>Mg(PO<sub>4</sub>)<sub>2</sub>·2H<sub>2</sub>O
Collinsite is a rare hydrated calcium magnesium phosphate, forming characteristic radial aggregates of acicular or bladed crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous to silky
- Streak
- White
- Density
- 3.03
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification A characteristic feature of collinsite is its forms of occurrence – most often radial or spherulitic aggregates of small, bladed or acicular crystals. Its relatively low hardness (3.5) and perfect cleavage are also helpful in identification. It reacts with acids. ## Distinguishing from Similar Minerals Collinsite can be confused with other phosphates that form radial aggregates, such as wavellite or strengite. However, wavellite is harder (3.5-4) and has a different chemical composition. Strengite has similar hardness but usually occurs in different mineral associations and has different optical properties. Accurate differentiation often requires chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms Collinsite crystals are typically elongated, bladed or acicular, consistent with the crystallographic b-axis. They form characteristic radial, spherulitic, fibrous aggregates, as well as rosetted clusters and layered coatings.
Geological environment
## Genesis Collinsite is a secondary mineral. It forms as a result of hydrothermal processes or weathering in phosphorus-rich sedimentary rocks, especially phosphorites. It can also form in caves as a product of reactions between solutions percolating through guano deposits and surrounding carbonate rocks. ## Mineral Associations This mineral often co-occurs with other phosphates. Depending on the location, it is accompanied by minerals such as anapaite, fairfieldite, whitlockite, carbonate-apatite, gypsum, quartz, calcite, dolomite, and various iron and manganese oxides. ## Localities Key collinsite localities worldwide include the area around François Lake in British Columbia (Canada), where it was discovered. Significant specimens also come from the Tip Top Mine in Custer County, South Dakota (USA), where it forms beautiful, white spherulites. It also occurs in Namibia, Australia (Iron Monarch mine), and Germany.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, spherical or radial aggregates of pure, white color and silky luster. Contrast with a dark matrix significantly enhances the visual appeal of the specimen. The absence of damage to the delicate, acicular crystals is also important. Specimens from classic localities, such as the Tip Top mine, are particularly sought after. ## Popular Localities The most famous collector specimens come from the Tip Top mine in South Dakota, USA. Specimens from the discovery locality in British Columbia, Canada, and from the Iron Monarch mine in South Australia are also highly valued.
Care and storage
## Cleaning Collinsite 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. Ultrasonic cleaners and steam cleaners should not be used. ## What to Avoid Collinsite is sensitive to acids, which can damage or dissolve it. It should be protected from contact with household and laboratory chemicals. As a relatively soft mineral, it is susceptible to scratching, so contact with harder minerals should be avoided. ## Storage It is recommended to store collinsite specimens in separate, padded boxes or display cases to prevent scratches and mechanical damage. It should be protected from dust and moisture. Fragile, acicular aggregates require particular care during handling and display.