Redondite
Chemical formula: AlPO<sub>4</sub>·2H<sub>2</sub>O
Redondite is a historical, discredited name for an iron-rich variety of variscite, which is a hydrated aluminum phosphate.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- White
- Density
- 2.5-2.6
- Cleavage
- Good on {010}
- Fracture
- Conchoidal
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of redondite as a variety of variscite is based on its characteristic forms of occurrence (reniform, spherical aggregates, crusts), vitreous-waxy luster, and green hues. It is relatively soft. However, definitive identification requires advanced studies, e.g., chemical analysis to confirm elevated iron content. ## Distinguishing from Similar Minerals Redondite (variscite) is most often confused with turquoise. It differs from turquoise by the absence of copper in its chemical composition, which can be verified by laboratory tests. Turquoise is also usually slightly harder. It can also be confused with chrysocolla or some forms of smithsonite. ## Crystal Forms Well-formed crystals are extremely rare. It almost always occurs in the form of massive, cryptocrystalline aggregates with a radial or fibrous structure, forming spherical, reniform, and botryoidal clusters, as well as veins and crusts.
Geological environment
## Genesis It is a secondary mineral, formed in the weathering zone of aluminum-rich rocks, as a result of the reaction of phosphate-rich solutions with aluminous minerals. It often forms near the Earth's surface. Its occurrences in guano deposits (bird droppings) are particularly well-known, where phosphates percolating through sediments reacted with the underlying rocks. ## Mineral Associations It co-occurs with other phosphate minerals, such as crandallite, wardite, strengite, as well as with clay minerals, quartz, chalcedony, and iron oxides (limonite). ## Localities The historical type locality is Redonda Island (Antigua and Barbuda). Generally, iron-rich variscite occurs in many places worldwide where variscite is present, including Utah and Nevada (USA) and Germany.
Rarity
Not very common
For collectors
## Quality Criteria Since "redondite" is a historical name for variscite, the evaluation criteria are the same. The most valued specimens are those with intense, uniform color (green or bluish-green), forming visually attractive shapes, e.g., well-defined spherical aggregates or veins in contrasting host rock. Purity, lack of fractures, and matrix also increase the specimen's value. ## Popular Localities Specimens from the historical locality on Redonda Island are primarily of historical significance. For variscite collectors in general, the most prized specimens come from the United States, especially from Utah (e.g., Clay Canyon, Little Green Monster mines) and Nevada.
Care and storage
## Cleaning Specimens should be cleaned only with lukewarm distilled water and a very soft brush or cloth. Ultrasonic and steam cleaners should be avoided, as they can cause cracking. ## What to Avoid Redondite (variscite) is sensitive to high temperatures, which can lead to permanent color change and dehydration. Contact with acids, solvents, detergents, and other chemicals should be avoided. Prolonged exposure to intense sunlight can cause fading. ## Storage Due to its relatively low hardness, specimens should be stored separately, wrapped in soft material, to avoid scratches from harder minerals. It is best to keep them in a dry and dark place.