Cyrilovite
Chemical formula: NaFe<sup>3+</sup><sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>·2H<sub>2</sub>O
Cyrilovite is a rare phosphate mineral, forming characteristic yellow-brown, vitreous crystals and aggregates.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous to resinous
- Streak
- Yellow
- Density
- 3.08-3.15
- Cleavage
- Good on {001}
- Fracture
- Uneven to conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Cyrilovite can be identified by its characteristic yellow to brown color, vitreous luster, and typical forms of occurrence – small, tabular or pyramidal crystals, often forming crusts and rosette aggregates. Its relatively low hardness (4 on the Mohs scale) is also a helpful feature. ## Distinguishing from Similar Minerals Cyrilovite is sometimes confused with other secondary iron phosphates, such as cacoxenite, strengite, or wardite. It differs from cacoxenite in crystal form (cacoxenite forms acicular, radial aggregates). It differs from strengite in color (strengite is usually violet or pink) and crystallographic system. Wardite, with which it forms a series, has very similar properties but contains aluminum instead of iron; a definitive distinction often requires chemical analysis. ## Crystal Forms Cyrilovite crystals are usually small and belong to the tetragonal system. They most often take the form of short, prismatic, tabular, or pyramidal crystals. They frequently occur as radial or rosette aggregates, as well as granular aggregates and massive crusts.
Geological environment
## Genesis Cyrilovite is a secondary mineral, forming in the oxidation zones of ore deposits, as well as through hydrothermal processes in granitic pegmatites. It forms as a result of the alteration of primary phosphate minerals, such as triplite or apatite, in the presence of iron-rich solutions. ## Mineral Associations This mineral often co-occurs with other phosphates, such as wardite (with which it forms an isomorphic series), apatite, strengite, rockbridgeite, dufrenite, phosphosiderite, as well as with quartz, microcline, albite, and limonite. ## Localities Important cyrilovite localities worldwide include the discovery site in Cyrilhof, Czech Republic; the Silver Coin mine in Valmy (Nevada, USA), which yields excellent crystals; the Sapucaia mine in Minas Gerais (Brazil); Hagendorf and Hühnerkobel in Bavaria (Germany); and also the vicinity of Krásno in the Czech Republic. Occurrences have also been reported in Australia (Iron Monarch mine) and Portugal.
Rarity
Rare
For collectors
## Quality Criteria Specimens with well-formed, sharp, and lustrous crystals of intense, lemon-yellow or orange color are most valued by collectors. Rich crusts covering the rock matrix and aesthetic, rosette aggregates are also highly prized. Contrast with associated minerals, such as white quartz, enhances the specimen's attractiveness. ## Popular Localities The localities in the USA (especially the Silver Coin mine in Nevada), Brazil (Sapucaia mine), and Germany (Hagendorf) are considered classic and yield the best specimens. Specimens from these locations command the highest prices in the collector's market due to the size and quality of the crystals.
Care and storage
## Cleaning Cyrilovite 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 or steam cleaning should not be used. ## What to Avoid The mineral is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It is also relatively soft and brittle, so it must be protected from impacts and scratches. Prolonged exposure to direct sunlight may not be advisable, although there is no detailed data on its photosensitivity. ## Storage Collector's specimens of cyrilovite are best stored in separate, padded boxes or display cases to prevent abrasion and mechanical damage. They should be protected from dust and moisture.