Mattagamite

Chemical formula: CoTe<sub>₂</sub>

Mattagamite is a rare cobalt telluride with a metallic luster, found in association with gold and other tellurides.

## Characteristics Mattagamite is a very rare mineral from the telluride group. It usually occurs as small, irregular grains or inclusions in other minerals, most often in calcite or quartz. It rarely forms well-developed crystals, and its identification requires specialized laboratory tests, such as electron microprobe analysis. It has a metallic luster and is opaque. Its color on a fresh surface is pinkish-white, which may darken over time. ## Physical Properties This mineral is characterized by a high density, approximately 8.93 g/cm³. Its Mohs hardness is estimated at 3.5. It has a metallic luster and is completely opaque. The streak is black. ## History and Name The name mattagamite comes from its discovery location – the Mattagami Lake mine in Quebec, Canada. The mineral was first described in 1971 by J. Rucklidge.

Properties

Mohs hardness: 3.5
Luster: Metallic
Streak: Black
Density: 8.93
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of mattagamite is impossible with the naked eye and requires advanced analytical techniques. Under a reflected light microscope (ore microscope), it exhibits characteristic optical properties. Final confirmation is chemical analysis, e.g., using an electron microprobe (EDS/WDS), which confirms the composition (cobalt and tellurium). ## Distinguishing from Similar Minerals It can be confused with many other metallic tellurides, sulfides, or arsenides, such as melonite, frohbergite, or safflorite, which often co-occur with it. The differences between them are subtle and can only be determined based on crystallographic data and precise chemical composition analysis. ## Crystal Forms Mattagamite crystallizes in the orthorhombic system. It usually forms anhedral (undeveloped) grains, not exceeding 100 micrometers in size, often as inclusions in other minerals.

Geological environment

## Genesis Mattagamite is a hydrothermal mineral. It forms in ore veins, usually in association with gold and other tellurides. Its formation is linked to low-temperature mineralization processes. ## Mineral Associations This mineral most often occurs in association with gold, altaite, melonite, tellurobismuthite, calaverite, petzite, as well as pyrite, chalcopyrite, sphalerite, galena, calcite, and quartz. ## Localities The most important and type locality is the Mattagami Lake mine in the Abitibi region of Quebec (Canada). It has also been reported in the Kidd Creek mine in Ontario (Canada) and several other localities worldwide, including Finland (Orijärvi) and Western Australia (Kalgoorlie), always as microscopic grains.

Rarity

Extremely rare

For collectors

## Quality Criteria From a collector's perspective, mattagamite is typically a systematic mineral and is primarily significant for specialized collectors of rare species (so-called "micromounters"). The value of a specimen is determined not by its aesthetics, but by the confirmed presence of the mineral through analysis, the richness of the mineral association, and its origin from the type locality. The most valuable samples are those where mattagamite is relatively "rich" and clearly visible under a microscope in association with other rare tellurides.

Care and storage

## Cleaning Due to its extreme rarity and typically microscopic grain size, mattagamite specimens are not subjected to cleaning in the traditional sense. Any cleaning of the host rock should be performed with the utmost care, preferably under a microscope, using only compressed air to remove dust. ## What to Avoid All mechanical cleaning methods (brushes, ultrasonics) and chemical cleaning should be avoided, as they can irreversibly damage or destroy the microscopic mineral grains. The specimen should be protected from moisture and sudden temperature changes. ## Storage Specimens containing mattagamite, which are subject to scientific research or advanced collecting, should be stored in specialized, padded "micromount" boxes, in stable room conditions, away from dust and vibrations.

Sources

IMA Mineral List (CNMNC)