Brumadoite

Chemical formula: Cu²⁺₃Te⁶⁺O₄(OH)₄·₅H₂O

Brumadoite is a very rare, secondary copper and tellurium mineral, forming microscopic, blue crystals with low hardness.

## Characteristics Brumadoite is a hydrated copper tellurate, occurring as very small, bladed or acicular crystals that rarely exceed 0.5 mm in length. It forms rosetted or radiating aggregates, as well as thin coatings and crusts. Its characteristic feature is an intense blue color. ## Physical properties This mineral is exceptionally soft, with a hardness of only 1 on the Mohs scale, meaning it can be scratched with a fingernail. It is transparent to translucent. Its density, calculated based on the chemical formula and unit cell parameters, is 4.768 g/cm³. ## Colors and varieties Brumadoite occurs exclusively in shades of blue. No color or commercial varieties are distinguished. ## History and name The mineral's name comes from its discovery location – the municipality of Brumado in the state of Bahia, Brazil. It was first described in 1993 based on specimens found in the local Pedra Preta magnesite quarry in the Serra das Éguas mountain range. ## Applications Due to its extreme rarity, small crystal size, and low hardness, brumadoite has no industrial application. It is of purely scientific significance and is sought after by specialized mineral collectors (so-called micromounters).

Properties

Mohs hardness: 1
Streak: pale blue
Density: 4.768
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Brumadoite is identified based on its unique combination of features: intense blue color, very low hardness (1 on the Mohs scale), characteristic, fine, bladed crystals forming rosetted aggregates, and specific occurrence (oxidation zones of magnesite deposits). ## Distinguishing from similar minerals It can be confused with other secondary blue copper minerals, such as azurite, linarite, or cyanotrichite. It differs from them primarily by its extremely low hardness. Azurite is much harder (3.5-4) and reacts with hydrochloric acid. Linarite is also harder (2.5). Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal forms Crystals are very small, elongated, with a bladed or acicular habit. They typically form radiating or rosetted clusters and aggregates, as well as thin coatings on the surface of the host rock.

Geological environment

## Genesis Brumadoite is a secondary mineral, formed in the oxidation zones of hydrothermal magnesite deposits containing tellurium and copper minerals. It forms as a result of the weathering of primary ores under specific chemical conditions. ## Mineral associations At its type locality, it co-occurs with magnesite, quartz, hematite, as well as other rare tellurates and tellurides, such as spiroffite, teineite, xocomecatlite, plumbogummite, and other secondary copper minerals. ## Localities The only confirmed and thoroughly described occurrence of brumadoite in the world is its type locality: Pedra Preta quarry, in the Serra das Éguas range, in the municipality of Brumado, in the state of Bahia, Brazil.

Rarity

Extremely rare

For collectors

## Quality criteria The collector appeal of brumadoite depends on several factors. Specimens with clearly formed, rich crystal aggregates of intense blue color, creating an aesthetic contrast with the light host rock (most often magnesite or quartz), are most highly valued. Due to the microscopic size of the crystals, the quality of their formation and the richness of the aggregate are key, rather than the size of an individual crystal. ## Popular localities The only source of collector specimens is the type locality in Brumado, Brazil. All specimens available on the market originate from this single location.

Care and storage

## Cleaning Brumadoite specimens are extremely delicate and sensitive. Mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Contact with water and any chemicals should be avoided. ## What to avoid - Water and cleaning solutions: they can damage or dissolve the mineral. - Vibrations and impacts: crystals are very brittle. - High temperatures and direct sunlight: they can lead to dehydration and color change. - Abrasion and touching: due to its hardness of 1, the mineral can be scratched with a fingernail. ## Storage Specimens should be stored exclusively in specialized, sealed micromount boxes to protect them from dust, mechanical damage, and humidity changes. Display is not recommended due to the mineral's sensitivity.

External references

https://www.mindat.org/min-38827.html