Grumiplucite
Chemical formula: Hg<sup>2+</sup>Bi<sup>3+</sup><sub>2</sub>S<sup>2-</sup><sub>4</sub>
Grumiplucite is an extremely rare mercury bismuth sulfide, forming acicular, metallic-gray crystals in hydrothermal vugs.
Description
## Characteristics Grumiplucite is a very rare mineral from the sulfosalt group, chemically a mercury bismuth sulfide. It forms very small, elongated crystals with a platy or acicular habit, rarely exceeding 1-2 millimeters in length. They usually occur as tangled or radiating aggregates in small rock cavities. The mineral has a metallic luster and a steel-gray to black color, which is typical for many sulfosalts. ## Physical Properties The luster of grumiplucite is strongly metallic. It is an opaque mineral. Its Mohs hardness has not been precisely determined due to the small size and rarity of the crystals. The density calculated based on its chemical composition and crystal structure is 7.66 g/cm³, making it a very heavy mineral for its size. ## Colors and Varieties This mineral is uniform in color, ranging from steel-gray to almost black. No color varieties or commercial forms are known. ## History and Name The name grumiplucite, approved in 1996 and described in 1998, is an acronym derived from the name of an Italian mineral collectors' group: **Gru**ppo **Mi**neralogico e **Plu**mbifero del **C**omprensorio di Gorno. Members of this group found the first specimens of the mineral. It was described by a team of mineralogists led by Paolo Orlandi. ## Uses Grumiplucite has no industrial applications. Its significance is purely scientific and collectible due to its extreme rarity and unique chemical composition.
Diagnostic features
## Identification Grumiplucite is identified by its appearance – metallic-gray, acicular or platy crystals. Key diagnostic features include its extreme rarity, very high density, and specific occurrence and paragenesis. Field identification is practically impossible, and specimens almost always require magnification for observation. ## Distinguishing from Similar Minerals It can be confused with other gray, metallic sulfosalts with an acicular habit, such as zinckenite, stibnite, or other rare bismuth sulfides. Definitive differentiation is almost exclusively possible based on chemical analysis (EDS) or X-ray diffraction (XRD). However, a key clue is its occurrence in paragenesis with other rare mercury minerals in the Vignola mine in Italy. ## Crystal Forms Crystals are strongly elongated along one axis, forming platy, acicular, or hair-like shapes. They often form chaotic, tangled aggregates or small radiating aggregates embedded in dolomite.
Geological environment
## Genesis Grumiplucite forms under low-temperature hydrothermal conditions. It crystallizes in small fissures and vugs within dolomitic rocks that have been subjected to solutions rich in sulfur, bismuth, and mercury. ## Mineral Associations This mineral co-occurs with dolomite, quartz, sphalerite, and galena. More importantly, it is accompanied by other, often equally rare sulfosalts, such as laffittite, routhierite, pierrotite, and zinckenite. ## Localities The only confirmed and most important locality for grumiplucite worldwide is its type locality – the Vignola-Fucina mine in Gorno, Val Seriana, Bergamo province, Italy. This is practically the sole source of specimens of this mineral.
Rarity
Extremely rare
Collector aspects
## Quality Criteria The collector's value of grumiplucite is primarily defined by its extreme rarity. Specimens rich in crystals, even if microscopic in size, are most highly prized. The presence of well-formed, sharp crystals forming aesthetic aggregates is also important. An additional advantage is its co-occurrence with other rare minerals from this locality. ## Popular Localities For collectors, the only significant source is the historic type locality in Gorno, Italy. Specimens from this location are highly sought after by specialized collectors of rare minerals and micromounts.
Care and storage
## Cleaning Grumiplucite specimens, typically micromounts, should only be dry-cleaned. A soft brush or a photographic air blower can be used to remove dust. Avoid any contact with water and chemical agents. ## What to Avoid The mineral is potentially brittle due to its perfect cleavage and low hardness. Ultrasonic cleaners, all acids, and detergents should be avoided. It should be protected from impacts and sudden temperature changes. As a mercury-containing sulfide, inhalation of dust during any processing should be avoided. ## Storage The best way to store specimens is to place them in a sealed micromount box, which protects them from dust and mechanical damage. They should be kept in a stable, dry environment.