Guanine
Chemical formula: C<sub>5</sub>H<sub>3</sub>(NH<sub>2</sub>)N<sub>4</sub>O
An organic mineral from the purine group, a main component of guano and the source of pearlescent luster in fish scales.
Properties
- Luster
- Pearly
- Density
- 1.72
- Cleavage
- Perfect on {010}
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Guanine can be identified based on its specific environment of occurrence – in guano deposits or as a biogenic product. Key visual features include a pearlescent luster on aggregate surfaces, white or yellowish color, and occurrence in the form of very fine, lath-like crystals, often forming powdery or crusty aggregates. ## Distinguishing from Similar Minerals It can be confused with other white, soft minerals found in guano deposits, such as brushite, newberyite, struvite, or uricite. It is distinguished from most of them by its strong pearlescent luster. However, definitive identification is difficult without advanced research methods, such as X-ray diffraction (XRD), due to the microscopic size of the crystals. ## Crystal Forms It forms very small, elongated, lath-like or tabular crystals. They usually occur as radial or disordered aggregates, as well as thin coatings, efflorescences, and earthy or powdery masses.
Geological environment
## Genesis This is a mineral of biogenic origin. It forms as a result of the decomposition of nucleic acids (especially guanine, one of the nitrogenous bases in DNA and RNA) contained in the excrement of seabirds and bats. It occurs in dried, often historical, guano deposits. It also forms in the skin and scales of fish, where its crystals are responsible for the silvery, pearlescent luster. ## Mineral Associations Guanine co-occurs with other minerals typical of guano deposits, such as uricite, brushite, monetite, whitlockite, and various phosphates. ## Localities The most important guanine localities are associated with large, historical guano deposits. The type locality is the Chincha Islands in Peru. It is also found on islands off the coast of Namibia, in bat caves (e.g., New Mexico, USA), and wherever large quantities of bird or bat excrement accumulate in dry climates.
Rarity
Not very common
For collectors
## Quality Criteria Guanine is a mineral of interest mainly to collectors specializing in organic minerals, systematics, or "micromount" specimens. It does not form large or visually spectacular crystals. The value of a specimen depends on confirmed identification, abundance on the matrix, and the presence of visible, even under a microscope, crystal structures. Samples from the type locality are most prized. ## Popular Localities For collectors, specimens from historical localities, primarily the Chincha Islands in Peru, are most desirable. Material from other confirmed localities, such as caves in the Guadalupe Mountains (New Mexico, USA), is also valued in specialized circles.
Care and storage
## Cleaning Guanine specimens are extremely delicate and usually occur as efflorescences or microcrystals. Wet cleaning should be avoided. Only very careful dust removal with a soft, dry brush or a gentle stream of compressed air from a distance is permissible. ## What to Avoid Guanine is an organic compound, sensitive to chemicals, high temperatures, and moisture. Contact with water, acids, bases, and solvents must be strictly avoided. Prolonged exposure to sunlight can lead to degradation. The mineral is flammable. ## Storage Specimens should be stored under stable conditions, in a dry place, away from direct sunlight and heat sources. The safest method is to place the specimen in a closed "micromount" box, which protects against physical damage, dust, and moisture.