Tellurium

Chemical formula: Te

Native tellurium is a rare, brittle, and crystalline semimetal with a tin-white color and metallic luster, found in hydrothermal veins.

## Characteristics Native tellurium is a chemical element and a mineral from the native elements group. In its pure form, it most often creates small, columnar or acicular crystals with a hexagonal cross-section, often gathered in radial or fan-shaped aggregates. It is also found in granular, massive forms, as well as dendritic coatings. It is characterized by a tin-white or lead-gray color, which can tarnish in air. It is a very brittle mineral. ## Physical Properties Tellurium is relatively soft, with a Mohs hardness of 2-2.5. It has a strong, metallic luster. It is opaque. The mineral's density is significant, ranging from 6.1-6.3 g/cm³. It exhibits perfect cleavage in one direction, parallel to the prism faces. ## Colors and Varieties This mineral does not form color varieties. Its color is constant, tin-white to lead-gray. Sometimes a dull, gray or black tarnish may appear on oxidized surfaces. ## History and Name The name tellurium comes from the Latin word *tellus* meaning "earth". The element was discovered in 1782 by Franz-Joseph Müller von Reichenstein in Zlatna (Romania), and named in 1798 by Martin Heinrich Klaproth. As a mineral, it was first described in the same location. ## Uses Native tellurium is primarily a sought-after collector's mineral. As an element, obtained mainly as a byproduct of copper and lead refining, it has a number of industrial applications. It is used in the production of alloys (e.g., with lead and steel to improve their machinability), in semiconductors, in photovoltaics (cadmium telluride), as well as in rubber and ceramics.

Properties

Mohs hardness: 2-2.5
Luster: Metallic
Streak: Gray
Density: 6.1-6.3
Cleavage: Perfect on {1010}
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Native tellurium can be identified by its tin-white color, strong metallic luster, high density, and characteristic crystal forms – prismatic, often in radial aggregates. Its low hardness (can be scratched with a fingernail) and perfect cleavage are also key diagnostic features. ## Distinguishing from Similar Minerals Tellurium is sometimes confused with other minerals with a metallic luster, such as antimony, native bismuth, stibnite, or galena. It differs from antimony and bismuth by its lower hardness and more prismatic crystal habit. Stibnite has a similar habit but is more lead-gray and often flexible. Galena crystallizes in the isometric system (cubes) and has perfect cleavage in three directions. ## Crystal Forms Tellurium crystals have a columnar or acicular habit, with a hexagonal outline. They are usually small. They often form radial, fan-shaped, stellate aggregates, as well as granular, massive concentrations and dendritic coatings on other minerals.

Geological environment

## Genesis Native tellurium is a mineral of hydrothermal origin. It forms at low and medium temperatures in ore veins, usually rich in gold and silver. It is one of the last minerals to crystallize in the formation sequence. ## Mineral Associations It most often co-occurs with native gold, native silver, as well as numerous tellurides such as sylvanite, krennerite, petzite, hessite, and altaite. It is also accompanied by sulfides (pyrite, galena, sphalerite) and quartz, calcite, and barite as gangue minerals. ## Localities Historically, the most important and type locality is Zlatna (formerly Sacarîmb) in Romania. Other significant occurrences include Cripple Creek in Colorado (USA), Kalgoorlie in Western Australia, and the Emperor mine on Viti Levu island (Fiji), which yields some of the world's best crystalline specimens. It also occurs in Mexico (Moctezuma mine) and Canada (Ontario).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, sharp crystals with a strong luster. Rich groups of crystals forming radial or stellate aggregates are particularly sought after. Specimens where native tellurium is clearly visible on a contrasting rock matrix, especially those co-occurring with native gold crystals, are also highly prized. ## Popular Localities The Emperor mine in Fiji is considered the source of the world's best, large, and well-formed tellurium crystals. Classic, though usually smaller, specimens come from historical localities in Romania (Zlatna) and the USA (Cripple Creek). Specimens from Kalgoorlie in Australia are also valued in the collector's market.

Care and storage

## Cleaning Native tellurium specimens should be cleaned with the utmost care due to their high brittleness and perfect cleavage. It is safest to use compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a very soft brush, avoiding any mechanical pressure. ## What to Avoid Tellurium is sensitive to chemicals, especially acids, in which it dissolves. Contact with all cleaning agents and acids should be avoided. The mineral is stable under normal conditions, but it should be protected from impacts and vibrations, which can cause it to break along cleavage planes. ## Storage It is recommended to store tellurium specimens in closed, padded collector's boxes to protect them from dust and mechanical damage. Due to its brittleness, it should not be stored in contact with harder minerals.