Tolstykhite

Chemical formula: Au₃S₄Te₆

Tolstykhite is an extremely rare gold sulfide and telluride, forming microscopic, metallic inclusions in other minerals.

## Characteristics Tolstykhite is a mineral with a metallic appearance, occurring as extremely small, anhedral (irregularly shaped) grains, typically ranging from 1 to 15 micrometers in size. The largest observed grains reached 50x150 micrometers. It is observed as inclusions within tolstykhite crystals, often in association with native gold and other tellurides. In reflected light, its color is gray. ## Physical Properties Due to the microscopic size of the grains, most physical properties of tolstykhite have not been precisely determined. Hardness and density are unknown. The mineral exhibits a metallic luster. ## History and Name The mineral was approved by the IMA in 2004 (IMA2004-035). Its name honors Nadezhda Dmitrievna Tolstykh (1923–2010), a Russian mineralogist and expert in the mineralogy of gold deposits and platinum group minerals from Siberia and the Russian Far East. It was discovered in the Aginskoye deposit in Kamchatka, Russia. ## Applications Tolstykhite has no industrial or commercial applications. Its significance is purely scientific and collectible, as an extremely rare gold mineral.

Properties

Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of tolstykhite is possible only through advanced laboratory methods, such as electron microprobe analysis (EMPA) in reflected light. Its characteristic feature is its occurrence as microscopic, gray, metallic inclusions within tolstykhite and other gold tellurides. ## Distinguishing from similar minerals It can be confused with other microscopic sulfides and tellurides, such as calaverite, krennerite, or sylvanite, with which it often co-occurs. Definitive differentiation requires chemical composition analysis, as optical properties in reflected light can be very similar. ## Crystal forms Tolstykhite forms exclusively anhedral, irregular grains and aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Tolstykhite forms under low-temperature hydrothermal conditions. It crystallizes in quartz-adularia veins associated with volcanism, in epithermal gold deposits. ## Mineral associations This mineral co-occurs with tolstykhite (in which it forms inclusions), native gold, calaverite, krennerite, sylvanite, petzite, hessite, pyrite, chalcopyrite, sphalerite, galena, quartz, and adularia. ## Localities The only confirmed locality of tolstykhite in the world is its type locality - the Aginskoye gold deposit, in the Sredinny Range on the Kamchatka Peninsula, in the Far Eastern Federal District of Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its microscopic nature, tolstykhite specimens are not evaluated for aesthetic appeal. Their collectible value lies solely in possessing an analytically confirmed specimen from the type locality. The most valuable samples are those where the presence of tolstykhite has been verified by scientific methods, and the mineral itself is visible (even as a tiny inclusion) under high magnification in association with other rare tellurides.

Care and storage

## Cleaning Specimens containing tolstykhite (usually inclusions in other minerals) should be cleaned with the utmost care, preferably using compressed air to remove dust. Mechanical and ultrasonic cleaning should be avoided. ## What to avoid Contact with chemicals, especially acids and bases, which can react with sulfides and tellurides, should be avoided. Due to its nature, it should be protected from scratching and abrasion. ## Storage Specimens containing tolstykhite are best stored in stable conditions, in sealed "micromount" boxes, to protect them from dust, mechanical damage, and sudden changes in humidity.

Sources

IMA Mineral List (CNMNC)