Donharrisite
Chemical formula: Ni<sub>3</sub>HgS<sub>3</sub>
Donharrisite is a rare nickel-mercury sulfide, forming tiny, metallic grains in serpentinites.
Properties
- Mohs hardness
- 3.5-4
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Identification of donharrisite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EDS/WDS) to confirm chemical composition (presence of nickel, mercury, and sulfur) and X-ray diffraction (XRD) to determine crystal structure. Visual identification, even under a microscope, is only preliminary and uncertain. ## Distinguishing from Similar Minerals Under a microscope in reflected light, it can be confused with other nickel sulfides, such as pentlandite, millerite, or heazlewoodite, which may coexist in the same environment. Definitive distinction requires chemical analysis, as donharrisite is characterized by its key mercury content. ## Crystal Forms This mineral forms exclusively very fine, irregular grains intergrown with other minerals. No well-formed crystals have been observed.
Geological environment
## Genesis Donharrisite forms as a result of low-temperature hydrothermal processes that affect ultramafic rocks, such as serpentinites. Its crystallization is associated with the circulation of sulfur-rich solutions that mobilize nickel from serpentinite rocks and mercury from an unknown source. ## Mineral Associations At the type locality (Le Prese, Switzerland), donharrisite coexists with heazlewoodite, magnetite, brucite, as well as other rare sulfides such as polydymite and violarite. These minerals are embedded in a matrix composed mainly of serpentine (antigorite). ## Localities The only confirmed and described locality of donharrisite occurrence in the world is its discovery site: a serpentinite quarry near Le Prese, in the Val Poschiavo valley, in the Canton of Graubünden, Switzerland.
Rarity
Extremely rare
For collectors
## Quality Criteria Donharrisite is a mineral of purely scientific and systematic importance; it does not form specimens of aesthetic value. The only criterion of value for specialized collections is the analytically confirmed presence of this mineral in a rock sample (a so-called micromount). A specimen is valuable if it contains rich concentrations of donharrisite grains that are clearly visible in microscopic studies and have been unambiguously identified.
Care and storage
## Cleaning Due to its extreme rarity and small grain size, donharrisite specimens are not subject to cleaning in the typical sense. Any interventions should be carried out exclusively under laboratory conditions by specialists. ## What to Avoid Contact with chemicals, especially acids, which can react with sulfides, should be avoided. Abrasion and any mechanical manipulation that could damage the microscopic grains embedded in the host rock should also be avoided. ## Storage Specimens containing donharrisite should be stored under stable conditions, in specialized containers that protect against dust, moisture, and mechanical damage. It is best to store them in their original host rock (matrix).