Huntingdonite

Chemical formula: Pb₂+₁₉Sb₃+₁₆As₃+₆S₂-₅₁Cl₂

Huntingdonite is an extremely rare, lead-gray sulfosalt mineral, discovered in the Madoc mine in Hastings County, Ontario (Canada).

## Characteristics Huntingdonite is a very rare, complex sulfosalt of lead, antimony, and arsenic. It occurs as small, anhedral (irregularly shaped) grains, usually not exceeding 100 micrometers in size. Its color is lead-gray, and in reflected light, it shows a creamy-white hue with a delicate greenish tint. This mineral is opaque and has a metallic luster. ## Physical Properties Due to the small size of its grains, most of huntingdonite's physical properties have not been precisely determined. Hardness and density are unknown. The mineral does not exhibit pleochroism or internal reflections. ## History and Name The mineral's name comes from its discovery location – the Madoc mine, which is situated in Huntingdon Township, Hastings County, Ontario, Canada. It was officially recognized by the International Mineralogical Association (IMA) in 2018 under number IMA2018-053. It was described by a team of researchers, including J.A. Mandarino and J.D. Grice.

Properties

Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of huntingdonite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EDS/WDS) for chemical composition and X-ray diffraction (XRD). Macroscopic visual identification is impossible due to the microscopic size of the grains and its resemblance to other sulfosalts. ## Distinguishing from Similar Minerals It can be confused with many other gray, metallic lead sulfosalts, such as boulangerite, jamesonite, or zinkenite, with which it often coexists. Definitive differentiation requires specialized chemical and structural analysis. ## Crystal Forms This mineral forms exclusively anhedral, i.e., irregular, embedded grains within the rock. No well-formed crystals have been observed.

Geological environment

## Genesis Huntingdonite forms as a result of hydrothermal processes in calcite veins cutting fluorite deposits. It is a late-stage crystallization mineral, forming at relatively low temperatures. ## Mineral Associations This mineral occurs in paragenesis with other, often rare, sulfosalts. In its type locality (Madoc mine), it coexists with boulangerite, jamesonite, madocite, laffittite, guettardite, twinnite, zinkenite, as well as with pyrite, sphalerite, fluorite, and calcite. ## Localities The only confirmed occurrence of huntingdonite in the world is its type locality: the Madoc mine (formerly known as the Moira mine), located in Madoc Township, Hastings County, Ontario, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, huntingdonite is not evaluated based on typical collector criteria such as size, color, or transparency. The value of a specimen lies in its extreme rarity and the richness and quality of associated minerals from the same locality. The most valuable samples are those where the presence of huntingdonite has been analytically confirmed. ## Popular Localities The only source of specimens is the historic Madoc mine in Canada. Research material comes from old, previously collected samples, as the mine has long been inactive.

Care and storage

## Cleaning Due to its extreme rarity and microscopic grain size, huntingdonite specimens are not cleaned in the traditional sense. Any attempts to clean the host rock should be carried out with utmost care, preferably under a microscope, using only compressed air to remove dust. ## What to Avoid Contact with any chemicals, acids, and ultrasonic cleaners should be avoided, as these could damage not only the mineral itself but also the associated minerals. The specimen should be protected from moisture and sudden temperature changes. ## Storage Huntingdonite specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, mechanical damage, and contamination. It is best to keep them in a dry place, away from direct sunlight.

Sources

IMA Mineral List (CNMNC)