Hotsonite
Chemical formula: Al<sub>5</sub>(S<sup>6+</sup>O<sub>4</sub>)(PO<sub>4</sub>)(OH)<sub>10</sub>·8H<sub>2</sub>O
Hotsonite is a hydrated aluminum phosphate-sulfate, forming soft, chalky white masses and aggregates.
Properties
- Mohs hardness
- 1
- Luster
- Earthy
- Streak
- White
- Density
- 2.06
- Cleavage
- Perfect on {0001}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Characteristic features of hotsonite include its chalky white appearance, very low hardness (approximately 1 on the Mohs scale), and occurrence in compact, earthy masses. It is soft to the touch and feels like a clayey material. ## Distinguishing from Similar Minerals Hotsonite can be confused with other white, earthy secondary minerals such as kaolinite, halloysite, or gibbsite. Distinguishing it from these minerals usually requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis, because their physical properties are very similar. ## Crystal Forms Hotsonite crystals are microscopic and appear as very small, thin, hexagonal plates. They form dense, felted aggregates that macroscopically look compact and amorphous.
Geological environment
## Genesis Hotsonite is a secondary mineral. It forms in the weathering (oxidation) zones of ore deposits, in an environment rich in aluminum, sulfates, and phosphates. At its type locality (Hotson Farm), it formed as a result of the weathering of sillimanite in the presence of solutions derived from the oxidation of pyrite and apatite. ## Mineral Associations This mineral co-occurs with other secondary and rock-forming minerals. At the discovery site, it was found in association with quartz, pyrite, chalcopyrite, sphalerite, goethite, jarosite, natrojarosite, apatite, sillimanite, wavellite, and strengite. ## Localities The most important and best-documented occurrence of hotsonite is its type locality – Hotson Farm 66, Namaqualand district, Northern Cape Province in the Republic of South Africa. This is the only confirmed locality for this mineral worldwide.
Rarity
Very rare
For collectors
## Quality Criteria The quality of hotsonite specimens is primarily assessed based on the purity and homogeneity of the material. As it is a microcrystalline mineral, individual crystals have no collector's significance. The most desirable specimens are clean, white, compact masses, free from impurities and clearly contrasting with associated minerals or host rock. ## Popular Localities The only source of hotsonite specimens is its discovery locality in the Republic of South Africa. For this reason, it is extremely rare on the collector's market and sought after mainly by collectors specializing in rare minerals or those from specific localities (so-called "locality collectors").
Care and storage
## Cleaning Hotsonite specimens are extremely delicate and fragile. Mechanical and water cleaning should be avoided. The safest way to remove dust is with a soft brush or a photographic air blower, without touching the mineral's surface. ## What to Avoid The mineral is very soft, so any contact with harder objects that could scratch or damage it should be avoided. It should be protected from water and moisture, as being a hydrated mineral, it can undergo changes. All chemicals should also be avoided. ## Storage It is recommended to store specimens in closed, padded collector's boxes to protect them from mechanical damage, dust, and humidity changes. It should not be exposed to direct sunlight.