Rruffite

Chemical formula: Ca₂Cu₂+(As₅+O₄)₂·₂H₂O

A rare arsenate mineral, hydrated calcium and copper arsenate, forming characteristic blue aggregates of acicular crystals.

## Characteristics Rruffite is a rare secondary mineral from the arsenate group. It occurs as small, acicular or bladed crystals, which most often form spherical or hemispherical aggregates and radial clusters. Specimens have a characteristic, intense, sky-blue or blue color, resembling some turquoises. Due to the small size of its crystals, it is primarily a mineral of interest to micromineral collectors. ## Physical Properties Rruffite crystals are transparent to translucent, with a vitreous luster. It is a relatively soft and brittle mineral. Its density, calculated based on the chemical formula and unit cell parameters, is approximately 3.63 g/cm³. ## Colors and Varieties This mineral is characterized by a uniform, sky-blue color in various shades, from light blue to azure. No color varieties or commercial names are distinguished. ## History and Name The name rruffite, approved by the International Mineralogical Association (IMA) in 2008, honors the RRUFF project – an initiative aimed at creating a comprehensive spectroscopic database of all known minerals. The mineral was first identified on specimens from the Mohawk Mine in San Bernardino County, California, USA, which is its type locality. ## Uses Due to its rarity and small size of occurrences, rruffite has no industrial application. It is solely an object of scientific interest and a valued acquisition in advanced collections of systematic minerals and microminerals.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Light blue
Density: 3.63
Cleavage: Indistinct
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of rruffite include its intense sky-blue color, vitreous luster, and typical occurrence in the form of radial aggregates composed of small, acicular crystals. The environment of occurrence is also crucial for identification – oxidation zones of copper and arsenic ore deposits. ## Distinguishing from similar minerals Rruffite can be confused with other blue secondary copper minerals, such as cyanotrichite, chalcanthite, or some varieties of aurichalcite. Cyanotrichite forms similar acicular clusters, but usually with a more silky luster. Chalcanthite is water-soluble. Final and certain distinction most often requires advanced analytical methods, such as Raman spectroscopy or EDS analysis. ## Crystal forms Rruffite crystals are strongly elongated, acicular or bladed, and almost always occur in characteristic, radial or spherical clusters (aggregates), forming crusts on the host rock.

Geological environment

## Genesis Rruffite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic deposits rich in copper and arsenic. It forms as a result of reactions of surface waters with primary sulfides and arsenides in an environment rich in calcium, originating from surrounding rocks (e.g., from calcite). ## Mineral associations This mineral co-occurs with other secondary minerals of the oxidation zone. In the type locality (Mohawk Mine), it was found in association with calcite, quartz, mimetite, chrysocolla, conichalcite, olivenite, and pharmacosiderite. ## Localities The most important and best-known occurrence of rruffite is its type locality – the Mohawk Mine in the Clark Mountain area, San Bernardino County, California, USA. It is a very rare mineral, and its occurrences in other locations worldwide have not yet been unequivocally confirmed and documented.

Rarity

Very rare

For collectors

## Quality criteria For collectors, especially those specializing in microminerals, the most desirable specimens are those with well-formed, large (for this mineral) and undamaged spherical aggregates of intense sky-blue color. Rich crusts covering a significant part of the rock matrix are also highly valued. Contrast with a white matrix (e.g., calcite) further enhances the aesthetic qualities of the specimen. ## Popular localities The only confirmed and recognized source of collectible rruffite specimens is the Mohawk Mine in California. Virtually all specimens available on the market come from this single locality.

Care and storage

## Cleaning Rruffite specimens should be cleaned with the utmost care. It is safest to use a soft brush to remove dust. Due to its arsenic content, wet cleaning should be avoided, as it could lead to partial dissolution of the mineral and contamination of the environment. If absolutely necessary, a minimal amount of distilled water can be used, and the specimen should be dried immediately. ## What to avoid The mineral is brittle and susceptible to mechanical damage. Contact with acids and other chemicals should be strictly avoided. Ultrasonic cleaners must not be used. Due to its arsenic content, inhaling dust from the mineral should be avoided, and hands should be washed after each contact with the specimen. ## Storage It is recommended to store specimens in closed, transparent boxes (micromount type), which protects them from dust, mechanical damage, and limits direct contact. Each specimen should be clearly labeled as an arsenic-containing mineral.

Sources

IMA Mineral List (CNMNC)