Pharmacoalumite

Chemical formula: KAl₄(As⁵⁺O₄)₃(OH)₄·₆.₅H₂O

Pharmacoalumite is a rare aluminum and potassium arsenate, forming small, cubic crystals with a vitreous luster, found in the oxidation zones of ore deposits.

## Characteristics Pharmacoalumite is a hydrated aluminum and potassium arsenate, belonging to the pharmacoalumite group. This mineral forms characteristic, small crystals with a regular, cubic shape, rarely exceeding 1 mm in size. It occurs as individual crystals, groups of crystals, as well as coatings and crusts. The crystals are usually well-formed, transparent to translucent, with a vitreous luster. ## Physical properties Pharmacoalumite is a relatively soft mineral, with a hardness of about 2.5 on the Mohs scale. Its density is approximately 2.6 g/cm³. It is brittle and exhibits an uneven fracture. No cleavage has been observed. The luster is described as vitreous. ## Colors and varieties This mineral is most often colorless or white. It can also take on pale yellow, light blue, light pink, or light grayish-green hues, depending on impurities. No named varieties are distinguished. ## History and name The name pharmacoalumite refers to its chemical composition – it contains pharmakon (Greek word meaning poison, in reference to arsenic) and aluminum. It was described as a new mineral in 1980 by Walenta, Zetti, and Appel. The type locality (locus typicus) was identified as the mine dumps at Ightem, in the Anti-Atlas Mountains in Morocco. ## Applications Pharmacoalumite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or secondary minerals.

Properties

Mohs hardness: 2.5
Color: White, pale yellow
Luster: Vitreous
Streak: White
Density: 0
Cleavage: Not reported, but other members of the group have good to fair cleavage.
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Isometric

Diagnostic features

## Identification A characteristic feature of pharmacoalumite is its perfectly formed, cubic crystals of small size. The vitreous luster and occurrence in paragenesis with other secondary arsenates in the oxidation zones of deposits are key indicators. Due to the small size of the crystals, final identification often requires advanced analytical methods, such as EDS analysis. ## Distinguishing from similar minerals Pharmacoalumite can be confused with other minerals from its own group, such as natropharmacoalumite (differs in sodium content instead of potassium) or pharmacosiderite. Distinguishing them based on visual characteristics is practically impossible and requires chemical analysis. It may also resemble other colorless or white secondary minerals, but its cubic crystal form is very diagnostic. ## Crystal forms Pharmacoalumite crystallizes in the isometric system, forming almost exclusively cubic crystals. These crystals occur individually, in small groups, or form druses and crusts on the host rock.

Geological environment

## Genesis Pharmacoalumite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in arsenic, especially arsenopyrite. It forms as a result of the reaction of arsenic-rich solutions with aluminum-containing minerals under conditions of low temperatures and pressures. ## Mineral associations This mineral often co-occurs with other secondary arsenates and sulfates. Its typical associated minerals include pharmacosiderite, scorodite, mansfieldite, conichalcite, olivenite, baryte, quartz, and iron oxides (limonite). ## Localities The most important and well-known occurrences of pharmacoalumite worldwide are the mines in the Bou Azzer region of Morocco, particularly Ightem, where it was discovered. It also occurs in the Cap Garonne mine in France, in the mines of the Lavrion region in Greece, in the Clara Mine in Germany (Black Forest), and in several locations in Cornwall, United Kingdom.

Rarity

Rare

For collectors

## Quality criteria The most prized specimens by collectors are those with sharp, well-formed, transparent crystals with a distinct cubic shape. Rich groups of crystals forming shiny druses on a contrasting rock matrix are also highly valued. Crystal size is a key factor – specimens with crystals exceeding 1 mm are considered exceptional. Color, although usually pale, can enhance attractiveness if it is, for example, a delicate shade of blue or pink. ## Popular localities Undoubtedly, the best and most sought-after pharmacoalumite specimens come from the type locality – Ightem in the Bou Azzer region of Morocco. Specimens from the Cap Garonne mine in France and Lavrion in Greece are also valued in specialized collections.

Care and storage

## Cleaning Pharmacoalumite specimens should be cleaned with the utmost care, using only compressed air to remove dust. Due to its softness and potential solubility, contact with water and any chemical agents should be avoided. ## What to avoid Absolutely avoid washing in water, ultrasonic cleaners, and using any acids or detergents, which can damage or dissolve the delicate crystals. The mineral is brittle, so it should be protected from impacts and vibrations. It should not be heated. ## Storage Collectible pharmacoalumite specimens are best stored in closed, padded "micromount" boxes, which protect them from dust, mechanical damage, and sudden changes in humidity.

External references

https://www.mindat.org/min-158.html