Khademite
Chemical formula: Al(S<sup>6+</sup>O<sub>4</sub>)F·5H<sub>2</sub>O
Khademite is a rare, hydrated aluminum sulfate with fluorine, forming colorless or white, tabular crystals that are water-soluble.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.03
- Cleavage
- Perfect on {010}, good on {100}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Helpful features in identifying khademite include its low hardness (2.5 on the Mohs scale), low density, vitreous luster, and tabular crystal habit. A key diagnostic feature is its water solubility, however, this is a destructive test. Occurrence in paragenesis with other secondary sulfates in a dry climate is also an important clue. ## Distinguishing from Similar Minerals Khademite can be confused with other white, soft secondary minerals, especially other water-soluble sulfates such as alunogen, epsomite, or halotrichite. Gypsum is also very soft, but crystallizes in a different system and is much less soluble. Certain distinction of these minerals based on visual features is very difficult and most often requires advanced studies, such as chemical analysis (detection of aluminum and fluorine) or X-ray diffraction (XRD). ## Crystal Forms Khademite crystallizes in the orthorhombic system. It most often forms thin to thick tabular crystals, often grouped into small aggregates, rosettes, or forming granular coatings and crusts on rock surfaces.
Geological environment
## Genesis Khademite is a secondary mineral, forming in the oxidation zones of ore deposits, especially in dry or desert climates. It forms as a result of the weathering of sulfide-bearing minerals (mainly pyrite) in the presence of aluminum-rich rocks, such as clay shales or volcanic tuffs. It often occurs as an efflorescence on mine workings walls or on rock surfaces. ## Mineral Associations This mineral co-occurs with other secondary sulfates, such as alunogen, copiapite, epsomite, gypsum, halotrichite, pickeringite, rozenite, and szomolnokite, as well as with pyrite. ## Localities The most important and type locality is Saghand in Yazd Province, Iran. Other confirmed occurrences include the Chuquicamata mine in the Antofagasta Region, Chile, and several locations in Utah, USA. It is a mineral found in very few places worldwide.
Rarity
Very rare
For collectors
## Quality Criteria As a very rare mineral, khademite is sought after mainly by specialized collectors. The value of a specimen is primarily determined by the quality and size of the crystals. Well-formed, sharply terminated, transparent tabular crystals forming rich aggregates are most prized. Aesthetic placement on a small rock matrix also enhances its appeal. ## Popular Localities The type locality, Saghand in Iran, is considered classic and provides the best specimens. Specimens from other localities, such as Chuquicamata in Chile, are also known in collections, but usually do not match the quality of those from Iran.
Care and storage
## Cleaning Khademite specimens are water-soluble, so **they must absolutely not be cleaned wet**. The only safe method is dry mechanical cleaning, using a soft brush or a stream of compressed air to remove dust and loose impurities. ## What to Avoid Avoid all contact with water and other liquids, as well as high humidity, which can cause slow dissolution and degradation of the mineral. Khademite is very soft and brittle, so it must be protected from impacts, scratching, and vibrations. ## Storage It is recommended to store specimens in tightly sealed, dry containers (e.g., "perky box" type). It is advisable to place a desiccant, such as silica gel, in the container. Display should be in a closed cabinet, away from sources of moisture and sudden temperature changes.