Stercorite
Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)Na(PO<sub>3</sub>OH)·4H<sub>2</sub>O
Stercorite is a rare phosphate mineral that forms in bat and seabird guano deposits.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- White
- Density
- 1.55
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of stercorite is its genesis (guano deposits) and physical properties: low hardness, water solubility, and a characteristic ammoniacal odor when moistened (which should not be done with a collector's specimen). It often occurs as unstable coatings and crusts. ## Distinguishing from Similar Minerals It can be confused with other phosphate minerals from guano deposits, such as hannayite or struvite. Struvite crystallizes in the orthorhombic system and has slightly different properties. Final differentiation often requires chemical analysis (XRD, EDS), especially for poorly formed specimens. ## Crystal Forms Stercorite crystallizes in the monoclinic system. Its crystals are very rare, usually small, with a tabular or prismatic habit. Most often, it forms compact, granular, earthy aggregates or crusts.
Geological environment
## Genesis Stercorite is a mineral of organic origin. It forms as a result of the reaction of phosphoric acid, released during the decomposition of seabird or bat droppings (guano), with sodium and ammonia in a low-humidity environment. It is a typical component of old, dried guano deposits. ## Mineral Associations It most often co-occurs with other phosphate minerals typical of guano deposits, such as struvite, hannayite, newberyite, as well as gypsum and calcite. ## Localities The most important and historical locality, from which the first described specimens originated, is the Chincha Islands in Peru. It also occurs in other places around the world where large guano deposits exist or existed, including Réunion Island, caves in South Australia (e.g., Wooltana), Namibia (e.g., Arnhem Cave), and Southern Africa.
Rarity
Rare
For collectors
## Quality Criteria Due to its rarity and instability, any well-preserved stercorite specimen is valuable. The most desirable specimens are those with visible, even small, crystals, which is extremely rare. For compact aggregates and crusts, the size of the specimen, its purity (lack of impurities), and well-documented locality are important. Association with other rare guano minerals is also valued. ## Popular Localities Historically, specimens from the Chincha Islands in Peru are most important, although they are practically unavailable today. Currently, specimens from caves in Namibia or Australia may appear on the collector's market.
Care and storage
## Cleaning Stercorite is water-soluble, so it must absolutely not be cleaned wet. Any contact with water, even a damp cloth, will cause damage or complete dissolution. Cleaning is only possible mechanically, dry, using a very soft brush or a stream of compressed air from a distance. ## What to Avoid Above all, avoid water and high humidity, which can cause the mineral to deliquesce. It should also be protected from all chemicals and acids. It is very soft and brittle, making it extremely susceptible to mechanical damage. ## Storage Stercorite specimens must be stored in conditions of controlled, low humidity. The best solution is a sealed container (e.g., a perky box) with a desiccant (silica gel) placed inside. Avoid exposing it to open air, especially on humid days.