Chihuahuaite

Chemical formula: Fe₂+Al₁₂O₁₉

Chihuahuaite is an extremely rare iron and aluminum oxide, a member of the magnetoplumbite group, found as microscopic inclusions in other minerals.

## Characteristics Chihuahuaite is an oxide mineral belonging to the hematite supergroup and the magnetoplumbite group. It occurs as hexagonal, tabular crystals with sizes not exceeding 200 micrometers. These crystals are typically intergrown with quartz or muscovite. Due to its microscopic size, visual features are difficult to observe without specialized equipment. ## Physical Properties Chihuahuaite crystals exhibit a metallic luster and are opaque. Their Mohs hardness is estimated at approximately 7.5, and the density calculated based on the chemical formula and cell parameters is 4.45 g/cm³. This mineral does not show cleavage, and its fracture is uneven. ## Colors and Varieties Chihuahuaite is black in color, and its streak is reddish-brown. No varieties are known. ## History and Name The mineral was discovered in a pegmatite near El Sauz, in the state of Chihuahua, Mexico, from which its name is derived. It was described in 2013 by Peter K.M. Megaw and collaborators, and its name and status as a new mineral were approved by the International Mineralogical Association (IMA) in 2012 (IMA2012-053). ## Uses Chihuahuaite has no industrial application and is of purely scientific interest and for highly specialized micromineral collectors.

Properties

Mohs hardness: 7.5
Luster: Metallic
Streak: Red-brown
Density: 4.45
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of chihuahuaite is only possible using advanced analytical methods, such as energy-dispersive spectroscopy (EDS/EDX) and X-ray diffraction (XRD), due to its microscopic size and occurrence as inclusions. Visual features, such as black color, metallic luster, and hexagonal crystal outline, can be observed under an electron microscope. ## Differentiation from Similar Minerals It can be confused with other black, metallic minerals from the magnetoplumbite group, such as magnetite, hibonite, or yimengite. Definitive differentiation requires chemical composition analysis, which will show the dominance of iron (Fe²⁺) and aluminum. ## Crystal Forms Chihuahuaite forms very small, hexagonal, tabular crystals, typically ranging from 50 to 200 micrometers.

Geological environment

## Genesis Chihuahuaite forms in granitic pegmatites. In its type locality (Mexico), it was found in a quartz-muscovite zone, indicating crystallization in the late stages of pegmatite evolution, under conditions of high aluminum activity. ## Mineral Associations This mineral coexists with quartz, muscovite, spinel, gahnite, hercynite, and hibonite. ## Localities The only confirmed occurrence of chihuahuaite in the world is its type locality: the El Sauz pegmatite in the municipality of Satevó, Chihuahua state, Mexico.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a chihuahuaite specimen is determined solely by the quality and abundance of crystals visible under a microscope. The most valuable samples are those where numerous, well-formed, hexagonal crystals can be identified, intergrown in a contrasting matrix (e.g., clear quartz or muscovite). Crystal size, even if microscopic, is also important – larger crystals are more desirable. ## Popular Localities The only source of specimens is the type locality in Chihuahua, Mexico, making them extremely difficult to acquire.

Care and storage

## Cleaning Due to their microscopic size and occurrence as inclusions, specimens containing chihuahuaite (i.e., the host rock) can only be cleaned very carefully, using a soft brush to remove dust. Avoid washing in water to prevent damage to the surrounding rock. ## What to Avoid Avoid contact with chemicals, ultrasound, and sudden temperature changes. Specimens should not be subjected to any invasive cleaning methods. ## Storage Specimens containing chihuahuaite should be stored in stable conditions, in a sealed "micromount" box, to protect them from dust and mechanical damage. Avoid exposure to moisture.

Sources

IMA Mineral List (CNMNC)