Gmalimite

Chemical formula: K₆&#₉₇₄₄;Fe₂+₂₄S₂-₂₇

Gmalimite is an extremely rare iron potassium sulfide, found exclusively as microscopic grains in pyrometamorphic rocks in Israel.

## Characteristics Gmalimite is a mineral of the djerfisherite group, belonging to the sulfide class. It occurs as anhedral (irregular), microscopic grains, usually not exceeding 50 micrometers in size. These grains are most often dispersed in the rock mass or form intergrowths with other minerals. The mineral is opaque and has a black color and metallic luster. ## Physical Properties Due to the microscopic size of the grains, many physical properties of gmalimite have not been precisely determined. It has a metallic luster and is opaque. Its density, calculated based on chemical composition and unit cell parameters, is 4.35 g/cm³. ## Colors and Varieties The mineral is uniformly black. No color varieties or commercial varieties have been distinguished. ## History and Name The name gmalimite comes from its discovery location – the Gmalim massif on Mount Hermon in Israel, which is its only known locality (type locality). It was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2017 (IMA2017-030). ## Applications Gmalimite has no practical application. It is solely an object of scientific research and interest for collectors specializing in rare minerals and micromounts.

Properties

Luster: Metallic
Streak: Black
Density: 4.35
Cleavage: None
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Identification of gmalimite is impossible without advanced analytical techniques. Due to its microscopic size and black color, it cannot be recognized visually. Certain identification requires chemical composition analysis using an electron microprobe (EDS/WDS) and crystal structure analysis by X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Visually, it is indistinguishable from other black, metallic minerals occurring in the same association, including the closely related djerfisherite. Differences can only be determined based on precise chemical analysis, which shows unique proportions of potassium, iron, and sulfur. ## Crystal Forms Gmalimite forms only very fine, anhedral grains. No well-formed crystals have been observed.

Geological environment

## Genesis Gmalimite forms under very specific and rare pyrometamorphic conditions. Its genesis is associated with the natural combustion of bituminous marls from the Ghareb Formation, leading to the formation of high-temperature rocks referred to as paralavas. The mineral crystallizes directly from local silicate-sulfide melts at temperatures exceeding 800°C. ## Mineral Associations This mineral coexists with other rare species typical of the pyrometamorphic environment of the Hatrurim Basin, such as anorthite, gehlenite, jasmundite, larnite, as well as other sulfides. ## Localities The only confirmed occurrence of gmalimite in the world is its type locality – the Gmalim massif within the Hatrurim Basin (the so-called Mottled Zone), on Mount Hermon in Israel.

Rarity

Extremely rare

For collectors

## Quality Criteria In the case of a mineral occurring exclusively in microscopic form, traditional evaluation criteria such as color or luster are of little significance. The collector's value of a specimen is determined by the abundance of gmalimite aggregates on the rock matrix, analytically confirmed mineral identity, and the presence of rare associated minerals. The most valuable samples are those originating directly from the research that led to the description of the species. ## Popular Localities The only source of gmalimite specimens is its discovery site in Israel. For this reason, all samples available on the collector's market come from this one, strictly defined locality.

Care and storage

## Cleaning Gmalimite specimens are typically micromounts that should not be wet cleaned. Any dust can only be removed with compressed air from a safe distance. Avoid touching the mineral surface. ## What to Avoid As a sulfide, gmalimite can potentially be sensitive to moisture and oxidation in the long term. Absolutely avoid contact with any chemicals, acids, and detergents. The specimen is very brittle due to its microscopic form of occurrence. ## Storage It is recommended to store specimens in specialized, tightly sealed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Each specimen should be precisely labeled.

Sources

IMA Mineral List (CNMNC)