Harmunite

Chemical formula: CaFe₃+₂O₄

Harmunite is a very rare calcium and iron oxide with a metallic luster, occurring in specific, high-temperature rock formations.

## Characteristics Harmunite is an oxide mineral, chemically a calcium and iron oxide. It forms small, prismatic or tabular crystals, often found in radial or rosette aggregates. Its most characteristic features are an intense, metallic luster and black color, giving it an appearance similar to some metal ores. ## Physical Properties This mineral is relatively hard, with a Mohs hardness of approximately 5.5. It has a black streak and is opaque. The density calculated from its chemical formula and unit cell parameters is 4.33 g/cm³. It exhibits good cleavage in two directions. ## Colors and Varieties Harmunite occurs exclusively in black. No colored varieties or trade names are known. ## History and Name The mineral's name comes from the locality Har-Amun (Mount Amun) within the Hatrurim Formation in the Negev Desert, Israel, where it was discovered. It was officially recognized by the International Mineralogical Association (IMA) in 2013. Its discovery is associated with research into the unique pyrometamorphic rock complex. ## Applications Due to its extreme rarity, harmunite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of systematic minerals and micromounts.

Properties

Mohs hardness: 5.5
Luster: Metallic
Streak: Black
Density: 4.33
Cleavage: Good on {010} and {100}
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Features facilitating the identification of harmunite include its black color, strong metallic luster, and characteristic small, prismatic or tabular crystals. However, a key indicator is its paragenesis – its occurrence in the unique rock environment of the Hatrurim Formation. ## Distinguishing from Similar Minerals Harmunite can be confused with other black, metallic minerals found in the same environment, such as hematite or magnesioferrite. Hematite is distinguished by its reddish-brown streak (harmunite's streak is black). Magnesioferrite crystallizes in the isometric system, often forming octahedra. Definitive identification is almost exclusively possible using advanced analytical methods, such as X-ray microanalysis (EDS) and X-ray diffraction (XRD). ## Crystal Forms Harmunite crystals are most often prismatic or tabular, with lengths not exceeding several tens of micrometers. They typically form radial or fan-shaped aggregates intergrown with other minerals.

Geological environment

## Genesis Harmunite forms under very specific conditions of pyrometamorphism, which is thermal metamorphism occurring at extremely high temperatures and low pressure. Its genesis is linked to the natural combustion of bituminous marls within the Hatrurim Formation in Israel. ## Mineral Associations This mineral co-occurs with other rare species characteristic of the Hatrurim Formation, such as ye'elimite, larnite, brownmillerite, as well as more common minerals like hematite, magnesioferrite, and fluorapatite. ## Localities The only confirmed locality for harmunite in the world is its type locality – the Hatrurim Formation (the so-called Mottled Zone) in the Negev Desert, Israel.

Rarity

Very rare

For collectors

## Quality Criteria For such a rare mineral, any specimen with well-formed, identifiable crystals is considered valuable. The most highly prized samples are those where harmunite forms distinct aggregates, and its crystals are clearly visible and contrast with the rock matrix. Co-occurrence with other rare minerals from this locality adds significant value. ## Popular Localities Collector specimens come exclusively from one location in the world – the Hatrurim Formation in Israel. They are available almost exclusively through specialized channels, among micromount collectors and scientific institutions.

Care and storage

## Cleaning Harmunite specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. If necessary, distilled water can be used, and then the specimen should be thoroughly dried. ## What to Avoid Avoid ultrasonic cleaners, which can damage crystals along cleavage planes. The mineral should not be exposed to strong acids or other aggressive chemicals. It is stable under normal conditions and does not require protection from light. ## Storage It is recommended to store specimens in closed "micromount" boxes or display cases to protect them from dust and mechanical damage. Due to the small size of the crystals, they should be handled with great care.

Sources

IMA Mineral List (CNMNC)