Burnsite

Chemical formula: KCd₂+Cu₂+₇O₂(Se₄+O₃)₂Cl₉

Burnsite is an extremely rare mineral from the selenite group, distinguished by its unique chemical composition and intense green color.

## Characteristics Burnsite is a very rare mineral from the oxysalt group, specifically a selenite containing potassium, cadmium, copper, and chlorine. It forms small, tabular or platy crystals of an intense, emerald-green color, which usually occur as fine aggregates, coatings, or as single, dispersed crystals on the rock surface. Due to its rarity and small crystal size, it is a mineral of primarily scientific and collector interest. ## Physical Properties Burnsite crystals exhibit a vitreous luster. They are transparent to translucent. The hardness on the Mohs scale is low, at 2, meaning it is a very soft mineral and susceptible to scratching. Its density, calculated based on the chemical formula and unit cell parameters, is approximately 4.15 g/cm³. ## Colors and Varieties This mineral is characterized by a vivid, emerald-green color. No color varieties or commercial forms are known. ## History and Name Burnsite was discovered in volcanic exhalation products (fumaroles) of the Tolbachik volcano on the Kamchatka Peninsula in Russia. It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 1999. Its name honors Peter C. Burns, a Canadian mineralogist and crystallographer from the University of Notre Dame, for his contributions to the study of mineralogy and crystal chemistry of oxygen-containing uranium and selenium compounds. ## Applications Due to its extreme rarity and small size, burnsite has no industrial applications. It is solely an object of scientific interest and a prized acquisition in advanced collections of rare minerals and microminerals.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Light green
Density: 4.15
Cleavage: Perfect on {001}
Fracture: Micaceous
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Burnsite is identified primarily by its unique appearance and occurrence environment. Key features include an intense emerald-green color, small, tabular crystals with a vitreous luster, and occurrence in volcanic fumarole products. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals At its type locality (Tolbachik volcano), burnsite can be confused with other green copper selenites, such as georgbokiite, sofiite, or ilinskite. Distinguishing it from these with the naked eye is practically impossible and requires specialized laboratory tests. Its characteristic chemical composition, simultaneously containing potassium, cadmium, and copper, is its main distinguishing feature. ## Crystal Forms Burnsite crystallizes as very small, thin, tabular or platy crystals, reaching sizes up to 0.2 mm. These crystals often form irregular aggregates, clusters, or coatings on the surface of the host rock.

Geological environment

## Genesis Burnsite is a mineral of volcanic origin, formed by sublimation from volcanic gases in high-temperature fumaroles. It crystallizes directly from hot vapors (exhalations) rich in selenium, copper, cadmium, potassium, and chlorine, depositing on the surfaces of volcanic rocks near fumarole vents. ## Mineral Associations This mineral co-occurs with other rare selenites and chlorides formed under similar conditions. At its type locality (Tolbachik volcano), it has been found in association with minerals such as sofiite, ilinskite, georgbokiite, halite, and sylvite. ## Localities The only confirmed locality for burnsite in the world is its type locality – the "Yadovitaya" fumarole on the Second Northern Breakout Cone of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of burnsite specimens is assessed primarily based on the richness and abundance of crystals on the rock matrix. Most prized are specimens with well-formed, undamaged crystals of intense, emerald-green color, forming dense aggregates. Due to the microscopic size of the crystals, the overall aesthetic of the specimen and the contrast with the substrate are also crucial. Specimens with well-studied associated minerals have additional scientific value. ## Popular Localities The only source of burnsite specimens is its type locality on the Tolbachik volcano in Kamchatka. Material from this location is extremely limited and rarely appears on the collector's market, coming mainly from old scientific collections and from collectors specializing in minerals from this locality.

Care and storage

## Cleaning Burnsite specimens should be handled with the utmost care. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove dust or compressed air from a safe distance. Avoid contact with water and any chemicals. ## What to Avoid Burnsite is a very soft mineral (hardness 2 on the Mohs scale), making it extremely susceptible to mechanical damage and scratching. It should be protected from contact with harder minerals. It is potentially soluble in acids. Avoid ultrasonic cleaners, chemical agents, and sudden temperature changes. ## Storage Burnsite specimens, typically in the form of microminerals, should be stored in specialized, sealed "micromount" boxes that protect them from dust, mechanical damage, and humidity. Avoid exposure to direct sunlight, although there is no evidence of fading.

Sources

IMA Mineral List (CNMNC)