Valleyite

Chemical formula: Ca<sub>4</sub>Fe<sup>3+</sup><sub>6</sub>O<sub>13</sub>

An extremely rare calcium and iron oxide, forming microscopic, black, metallic inclusions in metamorphic rocks.

## Characteristics Valleyite is a calcium and iron oxide, occurring as extremely fine, black, opaque grains or inclusions. Due to the microscopic size of its crystals, its visual characteristics are difficult to observe without specialized equipment. When observed in reflected light, it has a gray color and exhibits weak pleochroism. ## Physical Properties Valleyite crystals have a metallic to submetallic luster. Hardness and density have not been precisely measured due to the small size and rarity of the material. ## History and Name The mineral was approved by the IMA in 1987. Its name comes from its discovery locality – the Hatrurim Formation in the Ayalon Valley in Israel, locally known as "Biq'at Ayalon". ## Uses Valleyite has no practical or commercial applications. It is solely of scientific and collector interest due to its extreme rarity and specific formation conditions.

Properties

Luster
Metallic
Streak
Black
Cleavage
Good on {010}
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of valleyite is only possible using advanced laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD), on polished sections in reflected light. It is not possible to identify it with the naked eye or using simple tests. ## Distinguishing from similar minerals It can be confused with other opaque, black oxide minerals, such as magnetite, hematite, or ilmenite, which may coexist in the same rocks. Differentiation requires specialized micro-area analysis. ## Crystal forms Valleyite forms very fine, anhedral (irregular) grains, not exceeding 50 micrometers in size, occurring as inclusions in other minerals, mainly larnite.

Geological environment

## Genesis Valleyite forms under unique conditions of very high-temperature, low-pressure contact metamorphism, associated with the combustion of natural bitumen deposits. This process occurs in the carbonate rocks of the Hatrurim Formation. ## Mineral associations This mineral coexists with other rare minerals formed under similar conditions, such as larnite, brownmillerite, mayenite, hematite, magnetite, maghemite, and ye'elimite. ## Localities The only confirmed locality for valleyite in the world is its type locality in the Hatrurim Formation in Israel.

Rarity

Extremely rare

For collectors

## Quality criteria Since valleyite is a microscopic mineral, its value is determined not by the appearance of the mineral itself, but by the quality and richness of the host rock specimen. The most desirable samples are those with analytically confirmed presence of valleyite, originating from the type locality. These specimens are classified as "micromounts" and are of value only to specialized collectors of rare minerals. ## Market prices Specimens containing valleyite practically do not appear on the open market. Their circulation is limited to exchanges between scientific institutions and advanced collectors specializing in type-locality minerals and rare species.

Care and storage

## Cleaning Specimens containing valleyite are generally not cleaned due to the microscopic nature of the mineral and the risk of damaging the host rock. If absolutely necessary, compressed air can be used to remove dust. ## What to avoid Avoid contact with chemicals, acids, and ultrasonic cleaning, which could damage both the microscopic valleyite crystals and the surrounding minerals. ## Storage Store in stable conditions, away from dust and moisture, preferably in a labeled micromount box, to protect the delicate host rock.

Sources

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