Yecoraite

Chemical formula: Fe<sup>3+</sup><sub>3</sub>Bi<sup>3+</sup><sub>5</sub>O<sub>9</sub>(Te<sup>4+</sup>O<sub>3</sub>)(Te<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·9H<sub>2</sub>O

Yecoraite is a very rare bismuth and iron tellurate, forming microscopic, yellow, tabular crystals.

## Characteristics Yecoraite is a complex bismuth and iron oxide tellurate. It occurs as extremely small, tabular or bladed crystals, rarely exceeding 0.3 mm in length. These crystals form rosette-like aggregates, coatings, or appear as single, scattered flakes on the surface of the host rock. Due to the microscopic size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties Yecoraite crystals exhibit a luster described as subadamantine to resinous. They are transparent to translucent. Hardness and density have not been precisely measured due to the small size and rarity of the material. The mineral is brittle. ## Colors and Varieties This mineral is characterized by an intense, canary-yellow color. No varieties are known. ## History and Name The name Yecoraite comes from its discovery locality – the town of Yécora in Sonora State, Mexico. The mineral was first described by S.A. Williams in 1980 and approved by the International Mineralogical Association (IMA) in the same year. The type specimen is preserved at the Natural History Museum in London.

Properties

Luster
Resinous
Streak
Light yellow
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Characteristic features of Yecoraite include its canary-yellow color, tabular crystal habit forming rosette-like aggregates, and occurrence in oxidized zones of ore deposits rich in tellurium and bismuth. Final identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with other secondary yellow tellurium and bismuth minerals, such as tellurite or emmonsite. Yecoraite is distinguished by its specific, tabular crystal habit and unique chemical composition. In practice, distinguishing it from similar minerals without specialized equipment is impossible. ## Crystal Forms It forms very small, thin, tabular crystals with a hexagonal outline, often flattened. These crystals typically group into rosette-like or radiating aggregates.

Geological environment

## Genesis Yecoraite is a secondary mineral, formed in the oxidation zones (so-called iron caps) of hydrothermal ore deposits rich in tellurium and bismuth. It forms as a result of the weathering of primary tellurides. ## Mineral Associations It co-occurs with other minerals of the oxidation zone, such as quartz, hematite, goethite, as well as rarer tellurates and tellurites, e.g., schmitterite, emmonsite, mackayite, and eztlite. ## Localities The most important and type locality is the La Moctezuma (Bambolla) mine near the town of Moctezuma, in the municipality of Yécora, Sonora State, Mexico. This is the only confirmed locality from which well-characterized specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" type mineral, specimens with sharp, well-formed crystals creating aesthetic, rosette-like aggregates are most highly prized. The intensity and purity of the canary-yellow color also affect value. Contrast with the rock matrix and the absence of damage to the delicate crystals are important. ## Popular Localities The only source of collector specimens is the historic type locality – the La Moctezuma mine in Mexico. Material from this location is highly sought after by collectors specializing in rare minerals and "micromount" specimens.

Care and storage

## Cleaning Due to the extreme brittleness and small size of the crystals, mechanical cleaning is highly inadvisable. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Ultrasonic cleaners, steam cleaners, acids, solvents, and all chemical agents should be strictly avoided. The crystals are very delicate and can be damaged even by slight touch. Protect the specimen from moisture and sudden temperature changes. ## Storage Yecoraite specimens should be stored exclusively in specialized "micromount" boxes, which protect them from mechanical damage, dust, and moisture. Avoid exposure to direct sunlight, although there is no evidence of fading.

Sources

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