Evdokimovite
Chemical formula: Tl<sup>1+</sup><sub>4</sub>(V<sup>4+</sup>O)<sub>3</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>5</sub>·5H<sub>2</sub>O
Evdokimovite is an extremely rare thallium and vanadium sulfate, forming characteristic green crystals in volcanic fumaroles.
Description
## Characteristics Evdokimovite is a sulfate mineral that visually presents as aggregates of small, prismatic crystals with an intense green color. It is transparent and has a vitreous luster. It usually forms small aggregates, often with a radial structure, or occurs as chaotic encrustations on volcanic rocks. As a sublimation product from volcanic gases, its specimens are typically small (micromineral) and delicate. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent. Its density, calculated based on the chemical formula and unit cell parameters, is approximately 4.13 g/cm³. The Mohs hardness has not yet been determined due to the small size and rarity of the crystals. ## Colors and Varieties Evdokimovite occurs exclusively in one characteristic color – from light green to emerald green. No color varieties or commercial names are known. ## History and Name The mineral's name, approved by the International Mineralogical Association (IMA) in 2014, honors Mikhail Dmitrievich Evdokimov (1940-2013), a Russian mineralogist and petrologist from the St. Petersburg Mining Institute. He was recognized for his contributions to the study of the mineralogy of the Kola Peninsula. ## Uses Due to its extreme rarity and small crystal size, evdokimovite has no industrial application. It serves solely as an object of scientific research and a valuable acquisition for specialized collectors of systematic minerals and microminerals.
Diagnostic features
## Identification The key diagnostic feature of evdokimovite is its unique occurrence environment – it is a sublimation product in active volcanic fumaroles. Its intense green color, vitreous luster, and form of small, prismatic crystals forming aggregates are characteristic. However, final identification is only possible using advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Evdokimovite can be confused with other green secondary minerals occurring in the same environment, especially with other vanadium sulfates, such as markhinite. Distinguishing it based on visual features is practically impossible and requires specialized research equipment. ## Crystal Forms This mineral forms elongated, prismatic crystals of small size. These crystals often intergrow, forming radial or chaotic aggregates on the surface of the host rock (most often basaltic scoria).
Geological environment
## Genesis Evdokimovite forms under very specific conditions, as a crystallization product directly from hot volcanic gases (sublimate). It forms in fumarolic exhalation zones, at temperatures ranging from approximately 100 to 250°C. ## Mineral Associations This mineral occurs in association with other rare fumarolic minerals. It most commonly co-occurs with pauflerite, markhinite, shcherbinaite, bobjonesite, and hematite. ## Localities The only confirmed locality of evdokimovite in the world is its type locality – the second cinder cone of the Great Fissure Eruption of Tolbachik volcano on Kamchatka, Russia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria The quality of evdokimovite specimens, being a micromineral, is assessed based on several criteria. Specimens with well-formed, sharp, and as large as possible crystals are most highly valued. The intensity and purity of the green color are also important. Rich aggregates of crystals on a small rock matrix are more desirable than single, isolated needles. Association with other rare minerals from this locality adds additional value. ## Popular Localities The only source of evdokimovite specimens is the Tolbachik volcano on Kamchatka. All materials available on the collector's market originate from this single, classic locality for fumarolic minerals.
Care and storage
## Cleaning Evdokimovite specimens are extremely delicate and potentially toxic. They should absolutely not be wet-cleaned, as the mineral is water-soluble. The only permissible method for dust removal is the very careful use of a soft brush or a gentle stream of compressed air from a distance. ## What to Avoid Evdokimovite contains thallium – an element with high toxicity. Direct skin contact should be avoided, and above all, inhalation of dust and any risk of ingestion. The mineral is sensitive to moisture and temperature changes. It must not be exposed to direct sunlight, which can cause its degradation. All chemicals and ultrasonic cleaning should be avoided. ## Storage Evdokimovite must be stored in a sealed, closed container, preferably a "micromount" type, to protect it from moisture and environmental changes. The container should be clearly marked with a warning label indicating the toxicity of thallium. Store in a dry, temperature-stable place, away from people and animals.