Eddavidite
Chemical formula: Cu<sup>2+</sup><sub>12</sub>Pb<sup>4+</sup><sub>2</sub>O<sub>15</sub>Br<sub>2</sub>
Eddavidite is an extremely rare copper and lead oxybromide, forming black, submetallic crystals in volcanic exhalations.
Description
## Characteristics Eddavidite is a copper and lead oxybromide with a black color and opaque nature. It forms very small, prismatic or tabular crystals, not exceeding 0.1 mm in size. They usually occur as small aggregates and coatings. The mineral is characterized by a strong luster, described as submetallic to adamantine. ## Physical Properties The mineral's luster is submetallic to adamantine. It is opaque. Its density, calculated based on chemical composition and unit cell parameters, is 6.93 g/cm³. Hardness has not been determined. ## Colors and Varieties This mineral occurs exclusively in black. No colored varieties are known. ## History and Name Eddavidite was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2021. Its name honors two American mineralogists: Edward S. Grew (born 1944) and David I. Grew (born 1978), in recognition of their contributions to mineralogy. The type locality, the first place of discovery, is the fumaroles of Tolbachik volcano in Kamchatka, Russia. ## Uses Due to its extreme rarity and microscopic crystal size, eddavidite has no commercial or industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromineral collectors.
Diagnostic features
## Identification Identification of eddavidite is based on its unique occurrence environment (active volcanic fumaroles), black color, submetallic luster, and reddish-brown streak. Due to the microscopic size of the crystals, definitive confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Eddavidite can be confused with other black, opaque minerals found in fumaroles, such as tenorite (CuO) or georgbokiite (Cu₅O₂(SeO₃)₂Cl₂). Distinguishing it based on visual characteristics is practically impossible. Chemical analysis, which will show the presence of lead and bromine, as well as the characteristic reddish-brown streak, is crucial. ## Crystal Forms Eddavidite crystals have a prismatic or tabular habit. They are very small, reaching a maximum of 0.1 mm in length. Most often, they form clusters, aggregates, or thin coatings on the rock surface.
Geological environment
## Genesis Eddavidite is a fumarolic mineral. It forms through sublimation, crystallizing directly from hot volcanic gases rich in copper, lead, and bromine. Its formation temperature is high, which is typical for volcanic exhalations. ## Mineral Associations This mineral occurs in association with other rare fumarolic minerals. At the type locality, its co-occurrence with cotunnite, challacolloite, sanguite, georgbokiite, and avdoninite has been observed. ## Localities The only confirmed locality of eddavidite in the world is the fumaroles associated with the Second Fissure Eruption of Tolbachik volcano on the Kamchatka Peninsula, Russia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For such a rare micromineral as eddavidite, the main criterion of value is the richness of the specimen – meaning the quantity and degree of crystal development on the rock matrix. Specimens with clearly formed, though microscopic, crystals are highly prized. The presence of associated minerals, which confirm the paragenesis and origin of the specimen, is also of great importance. ## Popular Localities All known eddavidite specimens come from a single location in the world – Tolbachik volcano in Kamchatka. This is the only locality from which materials for research and collections are obtained.
Care and storage
## Cleaning Eddavidite specimens are extremely delicate and small. Any form of mechanical cleaning, including with water or compressed air, is highly risky and can irreversibly damage the crystals. It is recommended to leave the specimen in its untouched state. ## What to Avoid Avoid contact with water, acids, and other chemicals, as fumarolic minerals are often soluble or reactive. Protect the specimen from sudden changes in temperature, humidity, and direct sunlight, which can lead to its degradation. ## Storage The safest storage method is to place the specimen in a sealed "micromount" box, which protects it from dust, mechanical damage, and humidity fluctuations. Store in stable room conditions, away from light and heat sources.