Reynoldsite

Chemical formula: Pb₂+₂Mn₄+₂O₅(Cr₆+O₄)

Reynoldsite is an extremely rare lead manganese chromate oxide, forming dark, platy crystals on host rocks.

## Characteristics Reynoldsite is a very rare mineral from the oxide group, chemically classified as a lead manganese chromate oxide. It forms characteristic aggregates composed of platy or bladed crystals, often arranged subparallel or forming fan-shaped clusters. Specimens appear as thin coatings and crusts on the host rock. Its color is dark, ranging from reddish-brown to almost black, and its luster is described as submetallic to subadamantine. ## Physical Properties This mineral is characterized by a very high density, approximately 7.23 g/cm³ (calculated value based on chemical composition and crystal structure). Its Mohs hardness has not yet been determined. It is opaque in larger fragments, but its thin splinters are translucent, revealing a deep red color. It possesses perfect cleavage in one direction. ## Colors and Varieties Reynoldsite occurs in a uniform color range, from dark reddish-brown to brownish-black. No color varieties or commercial varieties have been distinguished. ## History and Name The mineral is named in honor of Robert C. Reynolds, Jr. (1928–2013), an American mineralogist specializing in clay minerals from Dartmouth College. It was officially described as a new mineral species in 2012. The type locality, from which the first studied specimens originated, is the Blue Bell claims in San Bernardino County, California, USA. ## Uses Due to its extreme rarity, reynoldsite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic mineral collections.

Properties

Luster: Sub-metallic to Adamantine
Streak: Reddish-brown
Density: 7.23
Cleavage: Perfect on {001}
Transparency: Opaque, Translucent in thin fragments
Crystal system: Triclinic

Diagnostic features

## Identification Helpful features for identifying reynoldsite include its characteristic reddish-brown to black color, submetallic luster, very high density, and reddish-brown streak. Its occurrence as aggregates of small, bladed crystals is also typical. It is often accompanied by yellow wulfenite. ## Distinguishing from Similar Minerals It can be confused with other dark and dense secondary minerals, such as goethite or some manganese oxides. It differs from goethite by a more reddish streak and often submetallic luster. Final confirmation of identity requires advanced analytical methods, such as EDS spectroscopy or X-ray diffraction (XRD). ## Crystal Forms Reynoldsite forms aggregates of flattened, bladed crystals up to several tens of micrometers long. These crystals arrange themselves into subparallel or fan-shaped packets, forming crusts and thin coatings on rock surfaces.

Geological environment

## Genesis Reynoldsite is a secondary mineral, formed in the oxidation zones (iron caps) of hydrothermal ore deposits, mainly lead. Its crystallization occurs as a result of the weathering of primary minerals in an environment rich in lead, manganese, and chromium. ## Mineral Associations This mineral most often occurs in association with other secondary minerals of the oxidation zone. At the type locality (California, USA), these include wulfenite, cerussite, chrysocolla, and goethite. In other localities, its co-occurrence with forate, mimetite, and phoenicochroite has been noted. ## Localities This is an extremely rare mineral, known from only a few localities worldwide. The most important locality, from which the best-formed specimens originate, is the type locality – the Blue Bell claims in San Bernardino County, California, USA. Its occurrence has also been confirmed at the Macrolite quarry in Arizona (USA) and in the Lavrion area in Greece.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with rich, visible under magnification, crusts of crystalline reynoldsite aggregates. An intense, reddish-brown color is highly valued. An additional advantage is a contrasting host rock and association with well-formed crystals of other minerals, especially wulfenite. ## Popular Localities By far the most sought-after and highly valued specimens come from the type locality in California (Blue Bell claims), which provided the material for the mineral's description.

Care and storage

## Cleaning Reynoldsite specimens should be cleaned with the utmost care, preferably using a soft brush to remove dust. If necessary, compressed air can be used from a safe distance. Avoid washing in water, and if absolutely necessary, use distilled water and immediately dry the specimen thoroughly. Never use ultrasonic cleaners. ## What to Avoid The mineral is sensitive to acids. It should be protected from scratches and impacts. As a mineral containing lead and chromium (in chromate form), it is potentially toxic. Avoid inhaling dust and wash hands after any contact with the specimen. ## Storage It is recommended to store reynoldsite specimens in separate, sealed collector boxes to prevent abrasion and contact with other minerals. It should be protected from dust and moisture. It is stable under normal room conditions.

Sources

IMA Mineral List (CNMNC)