Taramellite

Chemical formula: Ba<sub>4</sub>(Fe<sup>3+</sup>,Ti<sup>4+</sup>)<sub>4</sub>O<sub>2</sub>[B<sub>2</sub>Si<sub>8</sub>O<sub>27</sub>]Cl<sub>0-1</sub>

Taramellite is a rare barium silicate from the titanosilicate group, forming characteristic, almost black crystals with a strong luster.

## Characteristics Taramellite is a complex barium, titanium, and iron silicate, belonging to the group of rare minerals. It typically forms small, tabular or prismatic crystals, often aggregated into rosette-like or radial clusters. Its color ranges from dark brown to almost black, and on thin edges, it can be translucent reddish-brown. It is a brittle mineral with a characteristic, strong, almost metallic luster. ## Physical Properties This mineral is characterized by a hardness of 5-6 on the Mohs scale. Its luster is described as metallic to submetallic. It is opaque, becoming translucent only on very thin fragments. The density of taramellite is relatively high, approximately 4.9 g/cm³. ## Colors and Varieties The predominant and essentially only observed color of taramellite is dark brown to black. Thin fragments or crystal edges may exhibit reddish-brown translucence. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral is named in honor of the Italian geologist and paleontologist Torquato Taramelli (1845-1922), who was a professor at the University of Pavia. The mineral was first described in 1908 by Elio Tacconi based on samples from Candoglia, Italy.

Properties

Mohs hardness
5-6
Luster
Sub-Metallic
Streak
Red-brown
Density
4.88 - 4.96
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Characteristic features of taramellite include its black or dark brown color, strong, almost metallic luster, high density, and specific habit of small, tabular crystals forming aggregates. A reddish-brown streak is also an important diagnostic clue. ## Distinguishing from Similar Minerals It can be confused with other black, heavy minerals such as ilmenite, magnetite, or some tourmalines (schorl). It is distinguished from ilmenite and magnetite by the absence of magnetic properties and a reddish-brown streak (as opposed to black). It differs from schorl by its higher density, stronger luster, and crystal habit. ## Crystal Forms Taramellite crystals are usually small, with a tabular or short-prismatic habit. They often occur as radial or rosette-like aggregates, as well as granular aggregates within the host rock.

Geological environment

## Genesis Taramellite is a mineral of metamorphic origin. It forms under specific conditions in skarns or manganiferous gneisses that have undergone contact metamorphism. Its presence is associated with intrusions of igneous rocks into sedimentary rocks rich in barium and manganese. ## Mineral Associations This mineral coexists with other rare metamorphic minerals. Its typical associations include quartz, albite, barite, celsian, pyroxenes (e.g., hedenbergite), rhodonite, tephroite, and other barium and manganese minerals. ## Localities The most important and classic localities for taramellite are in Italy, in the Candoglia marble quarry in Piedmont (type locality) and in Liguria. It is also known from several locations in California (USA), especially from Fresno and Mariposa counties, where it occurs in metamorphic deposits. Other reported occurrences include Japan (Wessels Mine) and Wales (Benallt Mine).

Rarity

Very rare

For collectors

## Quality Criteria The most prized taramellite specimens are those with well-formed, sharp crystals exhibiting a strong luster, forming aesthetic, rosette-like aggregates. Contrast with a light host rock (e.g., quartz or marble) that highlights the dark crystals is important. Crystal size is crucial – larger, well-formed specimens are significantly rarer and more desirable. ## Popular Localities Specimens from the type locality in Candoglia, Italy, are of historical significance and valued by collectors. However, some of the world's best, well-formed taramellite crystals come from localities in California, such as Rush Creek (Fresno County) and Trumbull Peak (Mariposa County).

Care and storage

## Cleaning Cleaning is recommended only with a soft brush to remove dust. The use of water, especially with detergents, is not advisable due to the mineral's potential reactivity and the presence of chlorine in its structure. Ultrasonic vibrations can damage brittle crystals. ## What to Avoid Avoid contact with acids and other chemicals that may etch the mineral's surface. Taramellite is brittle, so protect it from impacts and falls. It should not be subjected to sudden temperature changes. ## Storage Taramellite specimens are best stored in separate, padded collector's boxes to prevent abrasion and mechanical damage. They should be protected from dust and moisture.

Sources

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