Yanomamite

Chemical formula: In₃+As₅+O₄·₂H₂O

Janomamite is a hydrated indium arsenate, a rare secondary mineral with a characteristic vitreous-green color, occurring as small crystals.

## Characteristics Janomamite is a hydrated indium arsenate belonging to the variscite group. It forms very small, most often isometric or short-prismatic crystals, rarely exceeding 0.5 mm. It usually occurs as encrustations or filling small voids in the rock. It is a transparent to translucent mineral with a vitreous luster. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 3-4. Its density is significantly higher than most similarly looking minerals, around 3.87 g/cm³. It is brittle and exhibits an uneven fracture. ## Colors and Varieties Janomamite occurs in shades from pale green to emerald green, sometimes it can also be colorless. No commercial or colored varieties have been distinguished. ## History and Name The mineral's name comes from the Yanomami, indigenous people of the Amazon inhabiting the areas where the Pitinga mine in Brazil – its discovery site – is located. It was described and approved as a new mineral in 1993 by G.R. Olivo, P.A. de Souza, A.C. Roberts, M.A. Cooper, and F.C. Hawthorne. ## Uses Due to its extreme rarity and small crystal size, janomamite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness: 3-4
Luster: Vitreous
Streak: White
Density: 3.87
Cleavage: Good on {010} and {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Janomamite is difficult to identify without advanced research methods. Preliminary identification is possible due to its characteristic green color, vitreous luster, and occurrence as very small, well-formed crystals in voids of greisen rocks. Its high density is a distinguishing feature, but difficult to verify on such small samples. Certain identification requires chemical analysis (EDS) to confirm the presence of indium and arsenic. ## Distinguishing from Similar Minerals It can be confused with other secondary green arsenates, such as conichalcite, olivenite, or pharmacosiderite. It is distinguished from them by its crystal habit (isometric or short-prismatic), and primarily by its chemical composition. It is also the zinc analogue of mansfieldite and the iron analogue of scorodite, from which it is distinguished by the presence of indium instead of zinc or iron. ## Crystal Forms Janomamite crystals are usually very small, with a bipyramidal or short-prismatic habit. They often form druses and crystal aggregates lining small cavities and fractures in the host rock.

Geological environment

## Genesis Janomamite is a secondary mineral, forming in the oxidation zone of tin (cassiterite) deposits in greisen rocks. It forms as a result of hydrothermal processes, where arsenic-rich solutions (derived from the oxidation of arsenopyrite) react with indium, released from other minerals, probably sphalerite. ## Mineral Associations It most often co-occurs with cassiterite, arsenopyrite, topaz, quartz, scorodite, sphalerite, chalcopyrite, and other sulfides. ## Localities The only confirmed and type locality for janomamite in the world is the Pitinga mine in Amazonas state, Brazil. This is one of the world's largest cassiterite deposits, known for the occurrence of many rare minerals.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, undamaged crystals of intense, emerald-green color. Samples where crystals form rich druses or are well-displayed against a contrasting background of the host rock (matrix) are highly rated. Due to the small size of the crystals, their quality and sharpness visible under magnification are crucial. ## Popular Localities The only source of janomamite specimens is the Pitinga mine in Brazil. All samples available on the collector's market come from this single locality, making them particularly sought after by collectors specializing in type locality minerals and rare minerals.

Care and storage

## Cleaning Specimens should only be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and potential solubility, contact with water and any chemical agents should be avoided. If liquid is necessary, the surface can be very carefully wiped with a cotton swab minimally moistened with isopropyl alcohol, ensuring that the liquid does not penetrate cracks. ## What to Avoid Ultrasonic cleaners, steam cleaning, acids, detergents, and immersion in water should be absolutely avoided. The mineral is sensitive to high temperatures, which can lead to its dehydration and destruction of its structure. It should be protected from direct sunlight, which can cause fading. ## Storage Janomamite specimens, due to their small size and fragility, are best stored in closed, padded "micromount" boxes. This protects them from mechanical damage, dust, and sudden changes in humidity. It should not be stored together with harder minerals.

Sources

IMA Mineral List (CNMNC)