Ferrisurite

Chemical formula: Pb₂+₂.₄Fe₃+₂Si₄O₁₀(CO₃)₁.₇(OH)₃·nH₂O

A very rare lead and iron silicate mineral, forming microscopic, platy crystals of a yellowish-brown color.

## Characteristics Ferrisuryte is a complex, hydrated lead and ferric iron silicate-carbonate. It occurs as very small, thin, platy or bladed crystals, which often form rosette-like, spherical, or radial aggregates. Due to its microscopic size, it is a mineral valued primarily by micromineral collectors. Individual crystals rarely exceed a fraction of a millimeter. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It is brittle and has perfect cleavage in one direction, which gives it a characteristic pearly luster on fracture surfaces. It is a heavy mineral due to its high lead content – its density is approximately 4.95 g/cm³. It is translucent. ## Colors and Varieties Ferrisuryte ranges in color from yellow, through yellowish-brown, to brown. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the "ferri" prefix is used due to the dominance of ferric iron, and the "suryte" part indicates its relation to structurally similar suryte, in which ferrous iron dominates. It was officially recognized by the International Mineralogical Association (IMA) in 1992. The type locality (locus typicus) is the Blue Bell deposits in San Bernardino County, California, USA. ## Uses Ferrisuryte has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 2
Luster: Pearly, Waxy
Streak: Pale yellow
Density: 4.95
Cleavage: Perfect on {001}
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of ferrisuryte include its yellowish-brown color, occurrence in the form of small, rosette-like aggregates with a pearly luster, and association with other secondary lead minerals. Its high density is also a helpful clue, although difficult to verify for microscopic specimens. ## Distinguishing from Similar Minerals Ferrisuryte can be confused with suryte, which is usually greenish and contains ferrous iron. It may also resemble other secondary minerals of the oxidation zone, such as microcrystalline mimetite (which is harder and has a different crystal habit) or dundasite (usually white and forming acicular aggregates). Definitive identification is possible almost exclusively using advanced analytical methods, such as EDS spectroscopy or X-ray diffraction (XRD). ## Crystal Forms It forms thin, platy crystals with a pseudohexagonal outline. These crystals aggregate into rosette-like, fan-like forms, as well as spherical clusters and thin coatings on the host rock.

Geological environment

## Genesis Ferrisuryte is a secondary mineral, forming in the oxidation zones (iron caps) of hydrothermal lead and zinc ore deposits, especially in arid climates. ## Mineral Associations It most often co-occurs with other minerals of the oxidation zone. At the type locality, it was found in association with suryte, cerussite, shannonite, chrysocolla, wulfenite, and iron oxides. In other localities, it is also accompanied by anglesite and galena. ## Localities The most important and well-known locality for this mineral is the Blue Bell Claims in California (USA). Significant specimens also come from the Kintore Opencut mine in Broken Hill (New South Wales, Australia). Apart from these two localities, it has only been reported in a few other places worldwide, including Greece and Namibia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of ferrisuryte specimens, being a typical micromineral, is assessed based on several criteria. Specimens with a rich covering of well-formed, sharp, and clearly defined rosettes or spherical aggregates are most highly valued. The size of these aggregates is also important – the larger they are, the more desirable the specimen. A contrasting rock matrix and association with other rare minerals enhance its attractiveness. ## Popular Localities The vast majority of specimens available on the collector's market come from two classic localities: Blue Bell Claims in California, USA (type locality) and Broken Hill in Australia. Specimens from Broken Hill are often considered to be of slightly better quality in terms of crystal development.

Care and storage

## Cleaning Ferrisuryte specimens are extremely delicate and brittle. They should only be cleaned with compressed air to remove dust. Any contact with water or a brush risks irreversible damage to the microscopic crystals. ## What to Avoid As a carbonate, ferrisuryte is sensitive to acids. Contact with chemicals, ultrasound, and sudden temperature changes should be avoided. Due to its significant lead content, it is potentially toxic – hands should be washed after any contact with the specimen. ## Storage It is recommended to store specimens in closed, padded "micromount" boxes to protect them from dust, light, and mechanical damage. It should not be stored in contact with harder minerals.

Sources

IMA Mineral List (CNMNC)