Tlalocite
Chemical formula: Cu<sup>2+</sup><sub>10</sub>Zn<sup>2+</sup><sub>6</sub>(Te<sup>4+</sup>O<sub>3</sub>)(Te<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>Cl(OH)<sub>25</sub>·27H<sub>2</sub>O
Tlalocite is a very rare, hydrated copper zinc hydroxychlorotellurate-tellurite, forming characteristic, sky-blue aggregates of acicular crystals.
Description
## Characteristics Tlalocite is a secondary mineral, recognizable by its characteristic sky-blue coloration. It occurs as delicate, acicular or fibrous crystals that form small, radial aggregates, bundles, and crusts. Due to the fine crystal habit and their fragility, individual needles are rarely visible to the naked eye, and the aggregates appear as felted or silky masses. ## Physical Properties This mineral is extremely soft, with a Mohs hardness of just 1, meaning it can be scratched with a fingernail. It has a vitreous luster and is translucent. Its specific gravity is approximately 3.25 g/cm³. It is very brittle and must be handled with the utmost care. ## Colors and Varieties The dominant and only known color of tlalocite is light blue, sky-blue, or bluish-green. The intensity of the color may vary slightly depending on the specimen. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from Tlaloc, the Aztec god of rain, lightning, and water, referencing its blue color. It was first described in 1975 by S.A. Williams. The type locality, from which the research material originated, is the Bambollita (La Oriental) mine in Moctezuma, Sonora, Mexico. ## Uses Due to its rarity, small size, and exceptional delicacy, tlalocite has no industrial applications. It is solely an object of scientific and collector interest.
Diagnostic features
## Identification Key diagnostic features of tlalocite are its unique sky-blue color, habit in the form of fine, acicular or fibrous aggregates, and extreme softness (Mohs hardness 1). Its paragenesis – co-occurrence with other, often rare, oxidized tellurium minerals – is also an important indicator. ## Distinguishing from Similar Minerals Tlalocite is sometimes confused with other secondary copper minerals of similar color and habit. - **Aurichalcite**: Has a similar acicular habit and bluish-green color, but is harder (2) and, as a carbonate, reacts vigorously with hydrochloric acid (destructive test). - **Xocomecatlite**: This is another copper tellurate, often green, but can have bluish hues. It usually forms spherical aggregates, not radial bundles. - **Spangolite**: Forms better-developed, tabular or dipyramidal crystals and is significantly harder (3). ## Crystal Forms Tlalocite exclusively forms very fine, elongated crystals with an acicular or fibrous habit. These crystals aggregate into forms resembling bundles, radial fans, rosettes, or create crusts and coatings with a felted texture.
Geological environment
## Genesis Tlalocite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal ore deposits rich in tellurium. It forms as a result of the weathering of primary copper and zinc tellurides under conditions of low temperature and high humidity. ## Mineral Associations This mineral occurs in association with other rare tellurium minerals, which is typical for its formation environment. It most commonly co-occurs with: tenorite, cuprite, azurite, malachite, as well as other tellurates and tellurites such as quetzalcoatlite, xocomecatlite, and teineite. Native tellurium is also often associated with it. ## Localities It is a very rare mineral, known from only a few localities worldwide. The most important and well-known occurrences are: - Bambollita (La Oriental) mine in Moctezuma, Sonora, Mexico – the type locality, from which the best specimens originate. - Historic mines in the Tombstone area, Cochise County, Arizona, USA (e.g., Emerald and Old Guard mines), known for the occurrence of many rare tellurium minerals.
Rarity
Very rare
Collector aspects
## Quality Criteria The collector appeal of tlalocite is determined by several factors. Specimens with rich, dense aggregates of acicular crystals of intense, sky-blue color are most highly valued. Contrast with the rock matrix and the presence of associated minerals, especially other rare tellurates, are also important. Due to extreme fragility, specimens without mechanical damage are rare and command higher prices. ## Popular Localities The most sought-after tlalocite specimens by collectors come from its type locality – the Bambollita mine in Mexico. Material from this locality is considered exemplary for the species. Specimens from Tombstone, Arizona, are also valued, often due to rich parageneses with other rare minerals.
Care and storage
## Cleaning Tlalocite specimens are extremely delicate and soft (Mohs hardness 1). Mechanical cleaning is highly risky. The only safe method for dust removal is to use a soft brush or a gentle stream of compressed air from a safe distance. Contact with water must be absolutely avoided. ## What to Avoid Tlalocite is a hydrated mineral, making it sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight, as this can lead to dehydration and, consequently, destruction of the crystal structure. All chemicals, detergents, and ultrasonic cleaners should be avoided. ## Storage It is recommended to store specimens in closed, stable conditions, preferably in "micromount" boxes or display cases that protect against dust, mechanical damage, and sudden changes in humidity. Specimens should be avoided from touching with fingers; tweezers should be used for handling.