Tomichite

Chemical formula: V<sup>3+</sup><sub>4</sub>Ti<sup>4+</sup><sub>3</sub>As<sup>3+</sup>O<sub>13</sub>(OH)

Tomichite is a rare vanadium, titanium, and arsenic oxide, forming small, black, prismatic crystals with a metallic luster.

## Characteristics Tomichite is a very rare mineral from the oxide group, chemically classified as a vanadium, titanium, and arsenic oxide with a hydroxyl group. It occurs as very small, prismatic or tabular crystals, rarely exceeding 1 mm in length. It typically forms granular aggregates or appears as single, disseminated crystals within the host rock. Its black, opaque nature and metallic luster are characteristic visual features. ## Physical Properties Tomichite is characterized by a high hardness, ranging from 6 to 7 on the Mohs scale, making it a relatively scratch-resistant mineral. It has a metallic luster and is opaque. Its density is significant, falling within the range of 4.3-4.4 g/cm³. The streak, which is the color of the powdered mineral, is black. ## Colors and Varieties This mineral is uniform in color and occurs exclusively in black. No color or commercial varieties are known. ## History and Name Tomichite was first discovered and described in 1976 by E.H. Nickel and I.E. Grey. The mineral is named in honor of Dr. John Tomich, an Australian geologist who first found this mineral in the Perseverance gold mine in Western Australia. The International Mineralogical Association (IMA) approved it as a new mineral species in the same year. ## Uses Due to its extreme rarity and occurrence as microscopic crystals, tomichite has no industrial applications. Its significance is purely scientific and collectible, being an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
6-7
Luster
Metallic
Streak
Black
Density
4.3-4.4
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Tomichite is identified by its black color, metallic luster, form of small, prismatic crystals, and specific occurrence environment. Due to its microscopic size, definitive identification requires advanced analytical methods such as chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other black, metallic minerals found in similar parageneses, such as ilmenite, magnetite, or rutile. Differentiation with the naked eye is practically impossible. Tomichite is distinguished by its unique chemical composition, containing vanadium, titanium, and arsenic simultaneously. ## Crystal Forms Tomichite crystals are typically very small, prismatic, often elongated and flattened. They form granular aggregates or occur as single, intergrown crystals in rock fissures.

Geological environment

## Genesis Tomichite is a hydrothermal mineral. It forms as a result of metasomatism in vanadium-rich carbonate-silicate rocks that have undergone low-grade metamorphism. It occurs in talc-carbonate veins cutting ultramafic volcanic rocks. ## Mineral Associations This mineral co-occurs with other vanadium and titanium minerals. At the type locality (Perseverance mine), it was found in association with native gold, pyrite, millerite, polydymite, gaspeite, talc, quartz, magnesite, chromite, rutile, nolanite, and priderite. ## Localities The most important and type locality for tomichite is the Perseverance gold mine (Agnew Mine) near Leinster in Western Australia. This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tomichite specimen primarily depends on the size and development of its crystals, which is rare. Specimens with clearly visible, sharp crystals contrasting with a lighter host rock are most valued. Due to the microscopic nature of the mineral, a rich association with other rare minerals is also crucial. ## Popular Localities The only source of collectible specimens is the type locality – the Perseverance mine in Western Australia. Specimens from this location are extremely difficult to acquire and represent a rarity in advanced systematic and "micromount" collections.

Care and storage

## Cleaning Tomichite specimens, due to their microscopic size and embedding in the host rock, usually do not require cleaning. If necessary, compressed air can be used to remove dust. Avoid contact with water and chemical agents. ## What to Avoid Avoid ultrasonic cleaners, strong chemicals, acids, and sudden temperature changes. Despite its relatively high hardness, the crystals are brittle and small, making them susceptible to mechanical damage. ## Storage Specimens should be stored in stable conditions, away from dust and moisture, preferably in a sealed "micromount" box. Protect from direct sunlight, although its light sensitivity is not known.

Sources

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