Brushite
Chemical formula: Ca(PO<sub>3</sub>OH)·2H<sub>2</sub>O
Brushite is a hydrated calcium phosphate, forming characteristic acicular crystals, often found in caves with bat guano.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous, Pearly on cleavage
- Streak
- White
- Density
- 2.328
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Brushite can be identified by its characteristic acicular or radial aggregates, low hardness (2.5 on the Mohs scale), and pearly luster on cleavage surfaces. It often occurs in specific environments, such as guano caves. ## Distinguishing from Similar Minerals It can be confused with other phosphates or sulfates, such as gypsum or monetite. It differs from gypsum by its perfect cleavage in one direction (gypsum has three) and often more radial habit. Monetite is chemically similar but anhydrous and has a different crystal habit. Final differentiation often requires chemical analysis (XRD). ## Crystal Forms It forms elongated, acicular, or tabular crystals, often gathered into radial, stellate, or sheaf-like aggregates. It also occurs as crusts, coatings, and earthy masses.
Geological environment
## Genesis Brushite is a mineral of sedimentary origin. It forms as a result of the reaction of phosphorus-rich solutions (derived from the decomposition of guano from seabirds or bats) with calcium carbonate from limestone rocks or corals. It is also an intermediate product in the phosphatization process of rocks. It can form in soils fertilized with superphosphates. ## Mineral Associations It often co-occurs with other phosphates, such as apatite, whitlockite, monetite, newberyite, as well as with gypsum and calcite. ## Localities Significant brushite localities are found in bat guano caves, e.g., in the Nullarbor region of Western Australia. It also occurs on islands with seabird guano deposits, such as Aves (Venezuela - type locality) or Monomoy (Massachusetts, USA). It is also found in caves in Mexico, Cuba, and Europe (e.g., Romania).
Rarity
Not very common
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, large, and transparent crystals, forming aesthetic, radial aggregates on a rock matrix. Undamaged specimens are desirable, which is rare due to the mineral's fragility. Contrast with dark host rock enhances visual appeal. ## Popular Localities Classic and prized localities include caves from the Yucatán Peninsula in Mexico, from which beautiful, radial aggregates originate. High-quality specimens have also been found in Western Australia (caves in the Nullarbor region) and in historical localities in the USA.
Care and storage
## Cleaning Brushite specimens are extremely delicate and sensitive to water. Wet cleaning should be avoided. Dust can be removed very carefully using a soft brush or a photographic blower. ## What to Avoid Contact with water, which can dissolve or damage the crystals, must be absolutely avoided. The mineral is very soft and brittle, so it must be protected from any impacts, scratches, and vibrations. Ultrasonic cleaners and all chemicals should also be avoided. ## Storage Brushite specimens are best stored in closed, padded boxes or display cases to protect them from dust, mechanical damage, and humidity changes. They should not be touched with bare hands.