Denningite

Chemical formula: CaMn₂+Te₄+₄O₁₀

Denningite is an extremely rare calcium and manganese tellurite, forming tiny, tetragonal crystals of an intense green color.

## Characteristics Denningite is a very rare mineral from the tellurite group, chemically classified as calcium and manganese tellurite. It occurs as very small, individual crystals, rarely exceeding 1 mm in size. These crystals most often have a dipyramidal form, and their surface is characterized by a strong, almost adamantine luster. Due to its rarity and small size, it is a mineral known mainly to specialists and advanced micromineral collectors. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 4. Its crystals are transparent to translucent. It has a high density, around 5 g/cm³, which is typical for tellurium-bearing minerals. The luster is described as adamantine to vitreous. ## Colors and Varieties Denningite occurs in a characteristic, bright green color, sometimes with a yellowish tint. No color varieties or commercial forms are known. ## History and Name The mineral was discovered in the Moctezuma mine in Mexico and described in 1963. Its name commemorates Reynolds McConnell Denning (1916–1967), a professor of mineralogy at the University of Michigan in the USA, who made significant contributions to the study of optical and crystallographic properties of minerals, including tellurides and tellurites. ## Applications Denningite has no industrial applications. Its significance is purely scientific and collectible, especially for collectors specializing in rare mineral species or tellurium minerals.

Properties

Mohs hardness: 4
Luster: Adamantine to vitreous
Streak: White
Density: 5.04
Cleavage: Imperfect on {001}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Denningite can be identified by its characteristic bright green color, tetragonal crystal form (usually dipyramidal), and very strong luster. Its origin is also key – it occurs exclusively in association with other rare tellurium minerals. ## Distinguishing from Similar Minerals It can be confused with other green tellurites, such as spiroffite or mackayite, which often co-occur with it. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Crystal Forms It forms small, well-developed dipyramidal crystals, reaching up to 1 mm in size.

Geological environment

## Genesis Denningite is a hydrothermal mineral. It forms in the oxidation zones of ore deposits where tellurium minerals are present. It develops as a product of the weathering of primary tellurides. ## Mineral Associations It most often co-occurs with other rare tellurium minerals, such as native tellurium, tellurite, paratellurite, emmonsite, mackayite, spiroffite, as well as quartz. ## Localities The only confirmed and classic occurrence of denningite in the world is the Bambolla mine (Moctezuma Mine) in Moctezuma, Sonora, Mexico. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly valued specimens are those with well-formed, sharp crystals of intense green color and strong luster. Aesthetic composition on the rock matrix and the presence of rare associated minerals are also important. Due to the microscopic size of the crystals, their quality under magnification is crucial. ## Popular Localities The only source of collectible specimens is the historic type locality – the Moctezuma mine in Mexico. Material from this location is extremely rare and sought after by specialized collectors.

Care and storage

## Cleaning Denningite specimens, due to their extreme rarity and small size, should be cleaned with the utmost care. It is recommended to use only compressed air to remove dust. Avoid contact with water and any chemical agents. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, acids, and sudden temperature changes. The mineral is soft and brittle, so it should be protected from impacts and scratches. ## Storage It is recommended to store specimens in specialized micromount boxes, which protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight.

Sources

IMA Mineral List (CNMNC)