Thoreaulite

Chemical formula: Sn<sup>2+</sup>Ta<sub>2</sub>O<sub>6</sub>

Thoreaulite is a rare oxide mineral containing tin and tantalum, valued by collectors for its unique chemical composition and well-formed crystals.

## Characteristics Thoreaulite is a rare tin-tantalum oxide mineral. It occurs as tabular or prismatic crystals, often forming twins and radial or fan-shaped aggregates. Its surface can be dull or covered with a coating. It is a heavy and brittle mineral. ## Physical Properties Thoreaulite has a hardness ranging from 5.5-6 on the Mohs scale. It has a very high density, approximately 7.9 g/cm³, which is noticeable even in small specimens. The luster on fresh fracture surfaces is resinous to metallic. The mineral is opaque. ## Colors and Varieties Its color is usually yellowish-brown, brown to almost black. Sometimes it can be reddish-brown. No distinct color varieties or commercial names are recognized. ## History and Name The mineral was first described in 1933 by Henri Buttgenbach. The name comes from Jacques Thoreau (1886-1973), a Belgian geologist from the University of Louvain, who first found this mineral in the Manono mine in the Democratic Republic of Congo. ## Uses Due to its rarity, thoreaulite has no industrial applications. It is solely an object of interest for collectors and scientists studying granitic pegmatites.

Properties

Mohs hardness
5.5 - 6
Luster
Resinous
Streak
Yellow-brown
Density
7.9
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Thoreaulite can be identified by its high density, characteristic resinous or metallic luster on fresh fracture surfaces, and tabular crystal habit. Its brown-yellow to black color and occurrence in pegmatites are also important indicators. ## Distinguishing from Similar Minerals It can be confused with other heavy, brown pegmatite minerals such as cassiterite, tantalite, or columbite. It differs from cassiterite by its lower hardness. From tantalite and columbite, it differs in crystal form and often a lighter, yellowish-brown color. However, final confirmation requires advanced analyses, e.g., X-ray diffraction (XRD). ## Crystal Forms Crystals are typically thin-tabular, flattened, with a rectangular or hexagonal outline. They often form twins, sometimes multiple, as well as fan-shaped and radial aggregates.

Geological environment

## Genesis Thoreaulite is a magmatic mineral, crystallizing in the late stages of the evolution of granitic pegmatites, especially those rich in lithium, tin, and tantalum (LCT-type pegmatites). ## Mineral Associations It most commonly co-occurs with cassiterite, tantalite, microlite, lepidolite, quartz, microcline, and albite. Its presence indicates a highly differentiated pegmatitic environment. ## Localities The most important and classic locality, from which the best specimens originate, is the Manono mine in Tanganyika Province, Democratic Republic of Congo. This mineral has also been found in pegmatites in Rwanda and in the Alto Ligonha region of Mozambique.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals with a distinct tabular habit are most valued by collectors. Impressive twinning and fan-shaped aggregates are also desirable. Specimens on a rock matrix, especially in association with other pegmatite minerals, are rated higher than single crystals. ## Popular Localities By far the most sought-after and classic specimens come from the Manono mine in the Democratic Republic of Congo. Material from this locality is considered exemplary for this species.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Water and any chemical agents should be avoided, as the mineral may react or be damaged. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is brittle, so it must be protected from impacts and falls. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in a dry place, preferably in a closed display box, away from moisture. To prevent scratches and mechanical damage, each specimen should be stored separately.

Sources

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