Hinsdalite

Chemical formula: Pb₂+Al₃(S₆+O₄)(PO₄)(OH)₆

Hinsdalite is a rare mineral from the phosphate, sulfate, and arsenate group, forming small, vitreous crystals ranging from colorless to greenish.

## Characteristics Hinsdalite is a complex lead aluminum hydroxyphosphate-sulfate, belonging to the beudantite group and the alunite supergroup. It most commonly occurs as very small, tabular or rhombohedral crystals, rarely exceeding 1-2 mm. It also forms rosette-like aggregates, radial aggregates, earthy masses, or coatings and crusts on other minerals. It is a transparent to translucent mineral, with a vitreous or dull luster. ## Physical Properties Hinsdalite crystals are brittle and have a Mohs hardness of 4.5. Its density is relatively high, ranging from 3.86 - 3.96 g/cm³, which is characteristic of lead-bearing minerals. The luster is usually vitreous, and on fracture surfaces, it can be resinous or dull. ## Colors and Varieties This mineral is most often colorless, white, gray, greenish, or yellowish. Its color depends on impurities and crystallization conditions. There are no named color varieties or commercial varieties. ## History and Name The name hinsdalite comes from Hinsdale County in Colorado (USA), where this mineral was first found and described. It was formally described by Esper S. Larsen, Jr. and W. T. Schaller in 1911 based on samples from the Golden Fleece Mine in Lake City. ## Uses Due to its rarity and small crystal size, hinsdalite has no industrial application. It is of scientific and collecting interest only, being sought after by collectors of rare minerals and micromounts.

Properties

Mohs hardness: 4.5
Luster: Vitreous, Resinous
Streak: White
Density: 3.86-3.96
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identifying hinsdalite in the field is difficult due to the small size of its crystals. Identification usually requires laboratory analysis (XRD, EDS). In a collection, it can be preliminarily recognized by the characteristic shape of small, rhombohedral or tabular crystals, vitreous luster, and co-occurrence with other minerals from the oxidation zones of ore deposits. ## Distinguishing from Similar Minerals It can be confused with other minerals from the alunite supergroup, such as corkite, beudantite, svanbergite, or woodhouseite, which have a similar appearance and occur in the same environment. Definitive distinction is almost exclusively possible using analytical methods that determine chemical composition (e.g., the ratio of phosphorus to arsenic or sulfur). ## Crystal Forms Hinsdalite crystallizes in the trigonal system. It most often forms small, sharply terminated rhombohedra or pseudo-cubic crystals. Tabular crystals are also found, often grouped into rosette-like or radial aggregates. It also occurs in the form of granular aggregates, earthy masses, and crusts.

Geological environment

## Genesis Hinsdalite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal ore deposits, especially those rich in lead, aluminum, phosphorus, and sulfur. It forms as a result of the reaction of acidic, sulfate-rich waters with primary minerals (such as galena) and surrounding rocks rich in aluminosilicates and phosphates (e.g., apatite). ## Mineral Associations It often co-occurs with other secondary minerals of the oxidation zone, such as pyromorphite, cerussite, anglesite, quartz, barite, fluorite, rhodochrosite, as well as other members of the alunite supergroup (corkite, beudantite, woodhouseite, svanbergite). ## Localities Important localities worldwide include the historical type locality in Hinsdale County, Colorado (USA); the Resuperferolitica mine in Silius, Sardinia (Italy), which yields good quality microcrystals; the Clara mine in the Black Forest (Germany); and occurrences in Australia (Dundas mine, Tasmania) and Great Britain (Caldbeck Fells mine, Cumbria).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, sharp, and lustrous crystals, even if they are small (micromounts). The transparency and clarity of the crystals and their aesthetic arrangement on the rock matrix are important. A contrasting matrix color (e.g., dark quartz) enhances the attractiveness of the specimen. Specimens from rare localities or with unusual colors (e.g., intensely green) are also more highly valued. ## Popular Localities Among the most sought-after by collectors are specimens from the Resuperferolitica mine in Sardinia, known for excellent microcrystals. Classic specimens from the type locality in Colorado (USA) and from the Clara mine in Germany, which supplies a wide range of rare secondary minerals, are also highly prized.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Ultrasonic cleaning is not recommended, as it can damage the brittle crystals. ## What to Avoid Avoid contact with acids and other strong chemicals, which can react with the mineral. Hinsdalite is brittle, so it must be protected from impacts and scratches. It should not be heated or exposed to sudden temperature changes. ## Storage The best way to store hinsdalite, especially micromount specimens, is to place them in sealed, padded boxes (so-called micromount boxes), which protect against dust and mechanical damage. Specimens should be stored in stable conditions, away from moisture.

Sources

IMA Mineral List (CNMNC)