Schieffelinite

Chemical formula: Pb₂+₁₀Te₆+₆O₂₀(OH)₁₄(S₆+O₄)·₅H₂O

Schieffelinite is a very rare, secondary lead tellurate-sulfate mineral, forming microscopic, colorless or white crystals.

## Characteristics Schieffelinite is a hydrated lead tellurate-sulfate, occurring as very small, prismatic or acicular crystals, rarely exceeding 1 mm in length. It typically forms radial aggregates, rosettes, or is disseminated in small vugs on the surface of the host rock. Due to its size, magnification is necessary for its observation. ## Physical Properties Crystals exhibit a luster described as vitreous to pearly. It is a very soft and brittle mineral. Due to the microscopic size of the crystals, most physical properties, such as density, are difficult to measure precisely and are based on calculated data. ## Colors and Varieties Schieffelinite is typically colorless to white. It has no known varieties. ## History and Name The mineral was discovered in Tombstone, Arizona (USA) and described in 1980. Its name honors Ed Schieffelin (1847–1897), a prospector and founder of the town of Tombstone, who played a key role in the discovery of the silver deposits there. The discovery of schieffelinite was the result of re-examining old mine dumps. ## Uses Schieffelinite has no industrial application. Its significance is purely scientific and collectible, being a coveted item for specialized collectors of rare minerals (so-called microminerals).

Properties

Mohs hardness: 1.5
Luster: Vitreous to Pearly
Streak: White
Density: 6.14
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Field identification of schieffelinite is practically impossible without specialized equipment. In a collection, it is recognized by its characteristic, small, acicular or prismatic crystals forming radial aggregates. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy, due to its co-occurrence with many other visually similar secondary minerals. ## Distinguishing from Similar Minerals Schieffelinite can be confused with many other secondary sulfates and tellurates, such as cerussite, anglesite, emmonsite, or hinsdalite, which often co-occur with it. Differentiation is based on the analysis of crystal form under high magnification and, ultimately, on chemical analysis. ## Crystal Forms It forms elongated, prismatic or acicular crystals, often terminated by sharp pyramids. These crystals group into radial aggregates, rosettes, or form chaotic clusters in rock fissures.

Geological environment

## Genesis Schieffelinite is a secondary mineral formed in the oxidation zones (so-called iron caps) of ore deposits, in arid or semi-arid climates. It forms as a result of the weathering of primary minerals containing lead (mainly galena) and tellurium (e.g., gold and silver tellurides). ## Mineral Associations It most often co-occurs with other secondary lead, zinc, and copper minerals. Typical associated minerals include: cerussite, anglesite, hinsdalite, emmonsite, bromargyrite, chlorargyrite, and native gold. ## Localities The most important and classic locality, from which the best specimens originate, is the mines in the Tombstone area, Cochise County, Arizona, USA. It has also been reported in several other locations worldwide, including the Grand Central mine in Pima County (Arizona, USA) and the Capillitas mine in Argentina, but specimens from these localities are much rarer and less known.

Rarity

Very rare

For collectors

## Quality Criteria The collecting appeal of a schieffelinite specimen depends on several factors. The most important is the abundance and size of the crystals – the larger and better-formed the needles or prisms, the more valuable the specimen. Rich, radial aggregates on a contrasting rock matrix are highly prized. The absence of damage to the delicate crystals and the aesthetic composition with associated minerals, such as small gold crystals, are also important. ## Popular Localities Specimens from the type locality – the historic mines in Tombstone, Arizona – are by far the most valued and sought after by collectors. Practically all material available on the collector's market originates from there.

Care and storage

## Cleaning Schieffelinite specimens should generally not be wet cleaned. If absolutely necessary, compressed air can be used very carefully to remove loose dust particles. Any form of mechanical cleaning or cleaning with liquids risks irreversible damage to the delicate crystals. ## What to Avoid Avoid contact with water and any chemicals. The crystals are extremely brittle and sensitive to shocks and temperature changes. Specimens should not be exposed to direct sunlight. ## Storage Schieffelinite specimens should be stored exclusively in specialized micromount boxes, which protect them from dust, shocks, and mechanical damage. Display should be done under a microscope.

Sources

IMA Mineral List (CNMNC)