Chromschieffelinite

Chemical formula: Pb₂+₁₀Te₆+₆O₂₀(OH)₁₄(Cr₆+O₄)·₅H₂O

Chromschieffelinite is a very rare lead chromium tellurate, forming microscopic, prismatic crystals of an intense orange color.

## Characteristics Chromschieffelinite is a hydrated lead chromate-tellurate-hydroxide. It occurs as extremely small, prismatic crystals, rarely exceeding 0.2 mm in length. These crystals are elongated and often form radial aggregates or chaotically arranged clusters on the surface of the host rock. Due to its microscopic size, it is a mineral primarily accessible to specialized collectors. ## Physical Properties Crystals exhibit a vitreous to adamantine luster. They are transparent to translucent. Due to the small size of the crystals, many physical properties, such as hardness or density, have not been precisely determined. ## Colors and Varieties The mineral is characterized by an intense, uniform color ranging from orange to orange-yellow. No varieties have been distinguished. ## History and Name Chromschieffelinite was first described in 1996 by Andrew C. Roberts and colleagues. Its name refers to its structural and chemical similarity to schieffelinite, with the addition of "chrom" due to the presence of chromium as a key component. The name of the parent mineral, schieffelinite, honors Richard Schieffelin, one of the founders of the town of Tombstone, Arizona, where both minerals were discovered. ## Uses Chromschieffelinite has no industrial applications. Its significance is purely scientific and collectible, being an object of interest due to its rarity and unique chemical composition.

Properties

Luster: Vitreous to Adamantine
Streak: Pale orange
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of chromschieffelinite is based on its characteristic orange color, prismatic crystal habit, and occurrence as small, radial aggregates. Its location and co-occurrence with other rare tellurates in the oxidation zones of ore deposits are crucial. ## Distinguishing from Similar Minerals It can be confused with other secondary lead minerals of similar color, such as wulfenite or crocoite. Differentiation requires chemical analysis (EDS/XRD) due to its microscopic size. It differs from schieffelinite (which is colorless to pale yellow) by the presence of chromium and a more intense color. ## Crystal Forms It forms slender, prismatic, elongated crystals, often pyramidally terminated. These crystals group into radial or randomly oriented aggregates.

Geological environment

## Genesis Chromschieffelinite is a secondary mineral, formed in the oxidation zones (gossans) of hydrothermal ore deposits rich in tellurium and lead. Its formation requires specific conditions, including the presence of chromium, which is a relatively rare element in such environments. ## Mineral Associations It most commonly co-occurs with other rare secondary minerals, such as schieffelinite, emmonsite, cerussite, anglesite, and also native gold. The presence of these associated minerals is an important diagnostic clue. ## Localities The only confirmed and type locality (localitas typica) for chromschieffelinite is the Grand Central mine in the Tombstone mining district, Cochise County, Arizona, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The most important criterion for evaluating a specimen is the quality and abundance of crystals on the rock matrix. Specimens with well-formed, undamaged, intensely colored crystals forming aesthetic aggregates are sought after. Contrast with the host rock color also enhances visual appeal. Due to the microscopic nature of the mineral, even small but crystal-rich fragments are highly valued. ## Popular Localities The only source of chromschieffelinite specimens is its historical type locality – the Grand Central mine in Tombstone, Arizona, USA. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Due to the extreme delicacy and small size of the crystals, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Avoid contact with water and any chemicals. ## What to Avoid Contact with water, acids, bases, and other solvents that could damage or dissolve the mineral must be strictly avoided. The crystals are very brittle and sensitive to vibrations and temperature changes. Do not expose the specimen to direct sunlight. ## Storage Chromschieffelinite specimens should only be stored in stable, sealed "micromount" containers to protect them from dust, moisture, and mechanical damage. They should be kept in a dry place with a constant temperature.

Sources

IMA Mineral List (CNMNC)