Bahianite

Chemical formula: Al<sub>5</sub>Sb<sup>5+</sup><sub>3</sub>O<sub>14</sub>(OH)<sub>2</sub>

Bahianite is an extremely rare, hard, and dense oxide mineral, found as pebbles ranging in color from white to light brown.

## Characteristics Bahianite is a very rare oxide group mineral, consisting mainly of aluminum and antimony oxides. It most commonly occurs as rounded, alluvial pebbles, rarely forming visible crystals. Its surface can be dull or earthy, but a fresh fracture reveals a vitreous to greasy luster. It is a hard mineral and relatively heavy for its appearance. ## Physical Properties It is characterized by a high hardness of 9 on the Mohs scale, placing it among the hardest minerals, just behind diamond. Its density is also high, ranging from 5.28 to 5.45 g/cm³. The mineral is usually translucent, rarely transparent. ## Colors and Varieties Bahianite ranges in color from white, through cream, yellowish, to light brown. Some specimens may exhibit a delicate asterism (star effect). No named varieties have been distinguished. ## History and Name It was first described in 1978 by Paul B. Moore and T. Araki. Its name comes from the state of Bahia in Brazil, where it was discovered in alluvium (river sediments) near the town of Paramirim. ## Uses Due to its extreme rarity, bahianite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals.

Properties

Mohs hardness
9
Luster
Vitreous, Greasy
Streak
White
Density
5.28 - 5.45
Cleavage
Good on {100}
Fracture
Conchoidal
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of bahianite are its exceptionally high hardness (9 on the Mohs scale), high density, occurrence as pebbles, and a white streak. Reaction to UV radiation (both shortwave and longwave) in the form of weak, chalky-white fluorescence can be helpful in identification. ## Distinguishing from Similar Minerals It can be confused with other hard, light-colored minerals found as pebbles, such as corundum (sapphire, ruby) or chrysoberyl. Differentiation requires specialized tests, such as density and hardness measurements. It differs from corundum by its slightly lower density and different chemical composition (presence of antimony). ## Crystal Forms Bahianite crystallizes in the monoclinic system. However, crystals are extremely rare and appear as small, columnar or tabular forms, often with visible striations. It is usually found as rounded grains and pebbles up to several centimeters in size.

Geological environment

## Genesis The exact genesis of bahianite is not fully understood. It is believed to have originally crystallized in aluminum-rich metamorphic rocks, which then underwent weathering. It is found secondarily in alluvial (river) sediments, where it arrived as a result of erosion and transport of parent rocks. ## Mineral Associations In alluvial sediments, it co-occurs with heavy minerals such as quartz, andalusite, kyanite, hematite, and eskolaite. ## Localities The only confirmed and most important occurrence of bahianite is in the alluvium of the Paramirim stream basin in the state of Bahia, Brazil. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with the largest mass and purity of color. Rarely found, well-formed crystals are exceptionally sought after and command significantly higher prices than typical pebbles. Specimens exhibiting asterism are also considered more valuable. ## Popular Localities The only source of collector specimens is its type locality - the Paramirim area in the state of Bahia, Brazil.

Care and storage

## Cleaning It is recommended to clean it only with a soft brush and distilled water. Due to its high hardness, it is scratch-resistant, but caution should be exercised. ## What to Avoid Avoid contact with strong acids and chemicals that could potentially damage the mineral's surface. Despite its high hardness, it should be protected from strong impacts that could cause cracks. ## Storage Bahianite specimens are best stored in separate, padded boxes or on stands to avoid contact with other minerals and potential mechanical damage. It is not sensitive to sunlight.

Sources

Read more