Reaphookhillite
Chemical formula: MgZn²⁺₂(PO₄)₂·4H₂O
Reaphookhillite is a rare, hydrated magnesium and zinc phosphate, forming colorless to white, bladed crystals.
Properties
- Mohs hardness
- 3
- Color
- Colorless
- Luster
- Vitreous
- Streak
- White
- Density
- 3.09
- Cleavage
- Parallel to {010}.
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Amateur identification of reaphookhillite is practically impossible. It requires specialized analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Preliminary identification in a collection is based on knowledge of the locality (Reaphook Hill quarry) and the characteristic morphology of small, bladed crystals in radial aggregates. ## Differentiation from Similar Minerals It can be confused with other secondary zinc phosphates, such as scholzite, tarbuttite, or hopeite, which may occur in similar environments. Scholzite often forms larger, more elongated crystals. However, definitive differentiation requires advanced laboratory studies. ## Crystal Forms Reaphookhillite forms thin, bladed crystals, elongated along one axis and flattened. These crystals combine into small, radial or stellate aggregates, as well as rosettes.
Geological environment
## Genesis Reaphookhillite is a secondary mineral that forms in the oxidation zones of zinc deposits. At its type locality (Reaphook Hill), it formed as a result of metasomatic alteration of sulfide-bearing dolomites, particularly sphalerite, under the influence of phosphorus-rich solutions. It forms in rock cavities and fissures. ## Mineral Associations This mineral co-occurs with other secondary phosphates and sulfates. At the type locality, it has been found in association with scholzite, tarbuttite, hopeite, parahopeite, sphalerite, pyrite, as well as rare minerals such as hillite and salmoite. ## Localities The only confirmed and described occurrence of reaphookhillite in the world is the Reaphook Hill quarry, located in the Flinders Ranges in South Australia.
Rarity
Extremely rare
For collectors
## Quality Criteria As a micromineral, reaphookhillite is valued primarily for its mere presence on a specimen. Samples with well-formed, sharp crystals forming aesthetic, radial aggregates are most highly prized. Contrast with the rock matrix and the absence of damage to the delicate crystals are also important. The size of the aggregates, even if measured in millimeters, significantly increases the value of the specimen. ## Popular Localities The only source of reaphookhillite specimens is its type locality – the Reaphook Hill quarry in South Australia. All specimens available on the collector's market originate from this single location.
Care and storage
## Cleaning Due to its extreme rarity and delicacy, reaphookhillite specimens should only be cleaned if absolutely necessary. Use compressed air (from a safe distance) to remove dust. Any contact with water or chemicals is highly inadvisable. ## What to Avoid Avoid contact with water, acids, detergents, and all other chemicals. The mineral is soft and brittle, so it must be protected from impacts, scratching, and vibrations. It should not be subjected to ultrasonic cleaning. Store away from heat sources and sudden temperature changes. ## Storage Reaphookhillite specimens, as microminerals, are best stored in specialized micromount boxes that protect them from dust, mechanical damage, and direct contact. Exposure should occur under stable humidity and temperature conditions, away from direct sunlight.