Deanesmithite

Chemical formula: Hg₁+₂Hg₂+₃S₂-₂OCr₆+O₄

Deanesmithite is an extremely rare mercury chromate-sulfide-oxide, distinguished by its complex composition and occurrence in only one locality worldwide.

## Characteristics Deanesmithite is a mineral ranging in color from dark reddish-brown to black. It occurs as very small, anhedral (irregular) or subhedral grains, usually less than 0.1 mm in size, and also as coatings on other minerals. Due to its microscopic size, its visual features are difficult to observe without magnification. ## Physical Properties This mineral is characterized by a very high density of 9.11 g/cm³, which is typical for mercury minerals. Its Mohs hardness is low, estimated at 2-2.5. It has an adamantine to submetallic luster. It is opaque, but very thin fragments can be translucent deep red. The streak of deanesmithite is reddish-orange. ## Colors and Varieties The primary and only known color of the mineral is dark red transitioning to brown and black. No color or commercial varieties have been distinguished. ## History and Name Deanesmithite was recognized as a new mineral in 1993. Its name honors Deane K. Smith (1926–2003), a professor of mineralogy at Pennsylvania State University, in recognition of his contributions to crystallography and mineralogy, including his work on the Powder Diffraction File (ICDD). ## Applications Due to its extreme rarity and microscopic size, deanesmithite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Mohs hardness: 2-2.5
Luster: Adamantine
Streak: Reddish orange
Density: 9.11
Cleavage: None
Transparency: Opaque, Translucent in thin fragments
Crystal system: Monoclinic

Diagnostic features

## Identification Key features for identifying deanesmithite include its extremely high density, reddish-orange streak, dark color, and adamantine luster. However, the most important indicator is its origin from the only known locality worldwide and its co-occurrence with other rare mercury minerals. ## Distinguishing from Similar Minerals Deanesmithite can be confused with cinnabar, with which it co-occurs. Cinnabar, however, has a significantly lower density (approx. 8.1 g/cm³) and a characteristic scarlet-red streak. Another similar mineral from the same locality is wattersite, which also contains chromium and mercury, but is black and has a yellowish-brown streak. Definitive identification is almost exclusively possible using advanced analytical methods (e.g., EDS, XRD). ## Crystal Forms This mineral does not form well-developed crystals. It is observed as microscopic, irregular grains and thin coatings on the surface of other minerals, mainly cinnabar.

Geological environment

## Genesis Deanesmithite forms in the oxidation zone of hydrothermal "hot-spring" type mercury deposits. It is a secondary mineral, forming under very low-temperature conditions. ## Mineral Associations This mineral occurs in association with other, often rare, mercury minerals. These most commonly include: cinnabar, corderoite, kenhsuite, perroudite, native mercury, wattersite, deweyldavidsite, and mosesite. ## Localities The only confirmed occurrence of deanesmithite worldwide is its type locality – the McDermitt Mine (also known as Cordero Mine) in Humboldt County, Nevada, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria Since deanesmithite occurs exclusively as microscopic grains and coatings, the collector's value of a specimen is primarily determined by the abundance of the mineral (quantity and "visibility" of grains on the rock matrix) and the aesthetics of its associated minerals, e.g., well-formed cinnabar. Any specimen with clearly visible, even under a microscope, deanesmithite grains is considered very valuable. ## Popular Localities The most valuable and only available specimens come from the McDermitt Mine in Nevada, USA. This is the only source of this mineral worldwide.

Care and storage

## Cleaning Deanesmithite specimens are extremely delicate and toxic. Wet cleaning is strongly discouraged. If absolutely necessary, dust can be removed very carefully with a soft brush or a photographic air blower. It is safest to leave the specimen uncleaned. ## What to Avoid **The mineral is highly toxic due to its high mercury content.** Avoid inhaling dust and direct skin contact. Wash hands thoroughly after any contact with the specimen. Do not heat it or expose it to any chemicals. Protect it from moisture and extreme temperatures. ## Storage Deanesmithite must be stored in a sealed, airtight container (e.g., a "membrane box"), with a clear label warning of its toxicity. Keep it away from children, pets, and food. It should be isolated from other minerals in the collection to prevent potential contamination.

Sources

IMA Mineral List (CNMNC)