Anthraxolite

Chemical formula: C

Anthraxolite is a hard, black, coal-like bituminous substance (mineraloid) with a vitreous luster, found in hydrothermal veins.

## Characteristics Anthraxolite is a mineraloid, meaning it is a naturally occurring substance that does not form crystals. Its appearance resembles anthracite (the highest quality hard coal), hence its name. It is characterized by an intense black color, a vitreous, almost pitch-like luster, and a conchoidal fracture, giving it an appearance similar to obsidian. It is opaque, hard, and brittle. It occurs as amorphous masses, fillings in veins and rock fissures, or as spherical aggregates. ## Physical Properties Its Mohs hardness ranges from 3 to 4, making it harder than most coals. The density is low, typically in the range of 1.3-1.4 g/cm³. Anthraxolite is brittle, and its fracture is distinctly conchoidal, smooth, and curved. It has an intense, vitreous to pitch-like luster. ## Colors and Varieties Anthraxolite is always black. No color varieties are distinguished. The name is sometimes confused with shungite, another black carbonaceous mineraloid, but these are distinct substances with different genesis and structure. ## History and Name The name "anthraxolite" was introduced by Elkanah Chapman in 1888. It refers to the Greek word "anthrax" (ἄνθραξ) meaning coal, due to its striking resemblance to anthracite. Chapman described it based on findings from the Sudbury area in Ontario (Canada). ## Uses Anthraxolite has no significant industrial applications. However, it is a valued and sought-after collector's material, especially specimens with well-formed, spherical shapes or those containing inclusions of other minerals, such as quartz.

Properties

Mohs hardness
3-4
Luster
Vitreous to resinous
Streak
Black
Density
1.3-1.4
Cleavage
None
Fracture
Conchoidal
Transparency
Opaque

Diagnostic features

## Identification Anthraxolite can be identified by its intense black color, very strong, vitreous or pitch-like luster, and characteristic conchoidal fracture. It is relatively lightweight. Unlike coal, it often occurs in veins cutting through sedimentary or metamorphic rocks, rather than in seams. ## Distinguishing from Similar Minerals It can be confused with anthracite, obsidian, or shungite. - **Anthracite** usually has a more subdued, submetallic luster and less frequently exhibits such a perfect conchoidal fracture. It also occurs in a different geological environment (seams in sedimentary rocks). - **Obsidian** (volcanic glass) is significantly harder (5-5.5 on the Mohs scale) and denser (approx. 2.4 g/cm³). - **Shungite** is very similar, but often has a more matte or submetallic surface. Definitive differentiation requires advanced compositional and structural analyses. ## Crystal Forms As a mineraloid, anthraxolite is amorphous and does not form crystals. It occurs as massive, reniform, spherical aggregates, and as fillings in veins and rock cavities.

Geological environment

## Genesis Anthraxolite forms as a result of thermal metamorphism of organic matter (bitumens) under hydrothermal conditions, at low to medium temperatures. It forms in fissures and veins cutting through various rock types, most commonly sedimentary (limestones, shales) and weakly metamorphosed rocks. Its formation is linked to the migration of petroleum or natural gas along faults, followed by their thermal transformation. ## Mineral Associations It often co-occurs with quartz (which frequently overgrows spherical forms of anthraxolite), calcite, dolomite, pyrite, sphalerite, and galena. In some localities, it is accompanied by other bitumens. ## Localities The most famous and classic occurrences of anthraxolite are in Canada, in the Sudbury region (Ontario), and in the Mohawk River Valley in New York State (USA), where it occurs in the form of the famous "Herkimer diamonds" (quartz crystals) with anthraxolite inclusions. Occurrences have also been reported in Germany, Czech Republic, Ukraine, and Russia.

Rarity

Not very common

For collectors

## Quality Criteria The most prized specimens by collectors are those exhibiting well-formed, spherical or globular shapes, especially if they form attractive groups. Specimens with a distinct, vitreous luster are also highly valued. Quartz crystals (especially the so-called Herkimer diamonds) containing black anthraxolite inclusions are exceptionally sought after. The contrast of transparent quartz with black anthraxolite creates very aesthetic compositions. ## Popular Localities Classic and most desirable specimens, especially those with inclusions in quartz, come from Herkimer County, New York, USA. Spherical aggregates with a high luster are also known from localities in Ontario, Canada.

Care and storage

## Cleaning Anthraxolite specimens are best cleaned dry, using a soft brush to remove dust. For heavier soiling, a damp cloth with distilled water can be used, followed by immediate and thorough drying of the specimen. Avoid prolonged immersion in water. ## What to Avoid Avoid contact with organic solvents, oils, and strong chemicals, which can damage its surface. Anthraxolite is a flammable material, so it must be kept away from open flames and high temperatures. It is brittle and sensitive to impacts and scratches. ## Storage Specimens should be stored in separate boxes or on a soft surface to prevent scratches and chipping. It does not require special protection from sunlight or humidity, but stable room conditions are always recommended.

External references

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