Burgessite

Chemical formula: Co²⁺₂(H₂O)₄(As⁵⁺O₃OH)₂·H₂O

Burgessite is a very rare, hydrated cobalt arsenate with an intense reddish-pink color, forming microscopic, acicular crystals.

## Characteristics Burgessite is a hydrated cobalt arsenate, occurring as microscopic, acicular or bladed crystals. It forms radial aggregates, rosettes, and crusts. Due to its cobalt content, it is characterized by a vivid reddish-pink color, which is its most recognizable feature. Specimens are usually very small, and individual crystals rarely exceed 1 mm in length, making them of interest primarily to micromount collectors. ## Physical Properties Burgessite crystals exhibit a vitreous luster. This mineral is relatively soft, with a Mohs hardness of approximately 3. It is transparent to translucent. Due to the small size of the crystals, most physical properties are difficult to observe without specialized equipment. ## Colors and Varieties Burgessite occurs in a characteristic reddish-pink to red hue. No color or commercial varieties have been distinguished. ## History and Name The mineral is named in honor of geologist Blair Burgess, who first found its specimens. Burgessite was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2010 (IMA2010-022). The discovery was made on the historic dumps of the Keeley-Frontier Mine in the South Lorrain area, Timiskaming District, Ontario, Canada. ## Uses Burgessite has no industrial application. Its significance is purely scientific and collectible, especially for collectors specializing in cobalt minerals, arsenates, or "micromount" specimens.

Properties

Mohs hardness
3.5
Color
Purplish pink with a slight brown tint
Luster
Vitreous
Streak
Colorless to pale pink
Density
2.93
Cleavage
{010} good and {001} fair
Fracture
Hackly
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Burgessite is identified by its unique form – radial aggregates composed of tiny, acicular crystals – and its intense, reddish-pink color. The locality of occurrence and associated minerals, such as erythrite, skutterudite, or cobaltite, are also key. ## Distinguishing from Similar Minerals Burgessite is visually almost identical to erythrite (Co₃(AsO₄)₂·8H₂O). Both minerals have a similar color, crystal habit, and occur in the same environments. Definitive differentiation is only possible using advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. ## Crystal Forms Crystals are elongated, acicular or bladed, with a rhombic cross-section. They typically form fan-shaped or radial aggregates and rosettes, as well as thin crusts on the host rock.

Geological environment

## Genesis Burgessite is a secondary arsenate mineral that forms in the oxidation (weathering) zones of ore deposits rich in cobalt and arsenic. It forms as a result of the reaction of surface waters with primary cobalt arsenides, such as skutterudite or cobaltite. ## Mineral Associations This mineral co-occurs with other secondary arsenates, primarily erythrite, as well as annabergite. It is found on primary ore minerals such as skutterudite, cobaltite, arsenopyrite, and also on calcite and quartz. ## Localities The only confirmed and described locality for burgessite in the world (type locality) is the dumps of the former Keeley-Frontier Mine in the South Lorrain area, Timiskaming District (Ontario, Canada). This is a historic silver and cobalt mining region.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly valued burgessite specimens are those with well-formed, rich aggregates of acicular crystals of intense, reddish-pink color. Contrast with a light host rock (matrix) and the absence of damage to the delicate needles are important. Due to the microscopic nature of the mineral, all specimens are evaluated as "micromounts." ## Popular Localities The only source of burgessite specimens is its type locality – the Keeley-Frontier Mine in Canada. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Burgessite specimens are extremely delicate and small. They should be cleaned only very carefully, using compressed air (from a safe distance) to remove dust. Any contact with water or a brush can irrevocably damage the tiny crystals. ## What to Avoid Avoid contact with water and all chemicals, including acids and detergents. The mineral is sensitive to shocks and abrasions. It should not be heated or exposed to prolonged strong light, although there is no evidence of fading. ## Storage Burgessite specimens, typically in "micromount" form, should be stored exclusively in dedicated, sealed perky boxes that protect them from dust, moisture, and mechanical damage. Avoid storage in humid environments.

External references

Sources

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