Coccinite

Chemical formula: Hg²⁺I¹⁻₂

Coccinite is a rare mercury(II) iodide, forming tiny, orange-red coatings and crystals, found in the oxidation zones of mercury deposits.

## Characteristics Coccinite is a secondary mercury mineral that typically occurs as earthy or powdery coatings and crusts. Less frequently, it forms very small, tabular or scaly crystals. Its most characteristic feature is an intense, orange-red to deep red color, which can resemble some iodine or mercury compounds. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2. It exhibits a greasy luster on crystal surfaces. It is translucent. Due to its occurrence in small aggregates, its density has not been precisely measured. ## Colors and Varieties Coccinite occurs in shades from orange-red to deep, almost blood-red. No color or commercial varieties are distinguished. ## History and Name The name coccinite comes from the Greek word *kokkinos* (κόκκινος), meaning "scarlet," which directly refers to its characteristic color. The mineral was first described in 1826 by Friedrich Mohs based on samples from Mexico. ## Uses Coccinite has no industrial application. Its significance is purely scientific and collectible, as a rare and interesting representative of iodides.

Properties

Mohs hardness: 2
Luster: Greasy
Streak: Red
Density: 0
Cleavage: On {001}.
Transparency: Translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Coccinite is primarily identified by its intense red color, very low hardness, and occurrence as small coatings and scaly crystals in the oxidation zones of mercury deposits. A red streak is also a characteristic feature. ## Distinguishing from Similar Minerals It can be confused with cinnabar (HgS), which also has a red color and occurs in similar environments. However, cinnabar is harder (2.5) and has a more intense, almost adamantine luster. Other red secondary minerals, like realgar, have different crystal forms and often different paragenesis. ## Crystal Forms Coccinite crystals, when visible, take the form of very small, thin, tetragonal tablets or scales. Most often, however, it forms earthy, powdery, or dusty aggregates and coatings on the host rock.

Geological environment

## Genesis Coccinite is a secondary mineral, formed in the oxidation zones of hydrothermal mercury deposits. It forms under dry and arid conditions as a result of reactions between iodine-rich solutions and mercury minerals, such as native mercury or cinnabar. ## Mineral Associations It often co-occurs with other mercury minerals, such as native mercury, cinnabar, calomel, eglestonite, as well as with iodargyrite, gypsum, and quartz. ## Localities The most important and historical locality (type locality) is the "Casas Viejas" region in Mexico. Other confirmed occurrences include mercury deposits in the Palatinate region of Germany and at Broken Hill in New South Wales, Australia.

Rarity

Very rare

For collectors

## Quality Criteria The most prized coccinite specimens are those with well-formed, even microscopic, crystals of intense red color, clearly contrasting with the host rock. Due to its rarity, even rich coatings of vivid color are considered valuable. Contrast with clear quartz or another rock enhances visual appeal. ## Popular Localities Specimens from the historical type locality in Mexico are classics, though rarely available on the market. Material from Broken Hill, Australia, is also highly valued by collectors specializing in rare minerals or minerals from that specific locality.

Care and storage

## Cleaning Coccinite specimens are extremely delicate and sensitive. Any mechanical or chemical cleaning should be avoided. If absolutely necessary, a stream of compressed air can be used from a safe distance to remove loose dust. ## What to Avoid Avoid contact with water, chemicals, and exposure to sunlight, which can cause its decomposition. The mineral is very soft, so touching and any abrasions should be avoided. As a mercury compound, it is toxic – avoid inhaling dust and wash hands after any contact. ## Storage Specimens should be stored in closed, airtight containers (e.g., "perky boxes"), away from light, moisture, and heat sources. It is best to store it in a dark and dry place to prevent its degradation.