Tellurium

Information about Tellurium (Native)

Native tellurium is one of the rarest and most scientifically significant of the native elements – a brittle, silvery-white metalloid that occurs in its pure elemental form only in a small number of gold-bearing epithermal deposits worldwide, and which has a discovery history more convoluted and disputed than almost any other element on the periodic table.

As a collector’s mineral it is valued for its rarity, its distinctive crystal habit, and the extraordinary geological company it keeps – native tellurium almost invariably occurs alongside gold tellurides and native gold, making fine specimens among the most scientifically interesting of any metallic minerals.

It typically forms as small, prismatic to acicular crystals, often striated lengthwise, sometimes in radiating or columnar groups, or as thin leaf-like or granular masses. It is silvery-white to tin-white on fresh surfaces, with a bright metallic lustre, and tarnishes slowly to yellowish-grey on exposure to air. It is notably brittle – far more so than the metals it superficially resembles – and has one perfect cleavage direction. It is very similar in appearance to native antimony and native bismuth, with which it can easily be confused in hand specimen.

Tellurium is a metalloid – meaning it has properties intermediate between metals and non-metals – and is a member of the chalcogen group, chemically related to sulphur and selenium. It is extremely rare in the Earth’s crust, with an average crustal abundance comparable to platinum, making it one of the least common of all the stable elements. This rarity is partly explained by its cosmic history: during the early formation of the solar system, tellurium readily formed volatile compounds that were lost to space before the Earth had fully cooled and solidified, depleting it relative to the abundance one would predict from nuclear physics alone.

Native tellurium forms in epithermal gold deposits – relatively shallow, low-temperature hydrothermal systems – where tellurium-bearing fluids deposit native tellurium and gold telluride minerals together in veins. It is almost always found in association with calaverite, sylvanite, petzite, krennerite, and other gold and silver tellurides, as well as with native gold, pyrite, and quartz.

Uses and History

The discovery history of tellurium is one of the more tangled in the history of science. The element was first encountered in gold ore from the mines at Kleinschlatten (now Zlatna) in Transylvania, Romania, in 1782 by the Austrian mineralogist Franz-Joseph Müller von Reichenstein.

After more than fifty exhaustive tests over three years, Müller established that the ore contained an unknown element, but his findings were published in an obscure journal and went almost entirely unnoticed. He referred to the material as aurum paradoxum (paradoxical gold) and metallum problematicum (problem metal). In 1789 the Hungarian scientist Pál Kitaibel independently discovered the same element, but subsequently gave priority to Müller. It was not until 1798 that Martin Heinrich Klaproth, the great German analytical chemist, formally isolated the element, confirmed Müller’s findings, and named it tellurium after the Latin tellus, meaning earth.

Industrially, tellurium is a strategic material of growing importance. It is used as a minor additive in steelmaking and copper alloys to improve machinability; as a vulcanising agent in rubber; as a colouring agent in glass and ceramics; and – most significantly for the modern world – as a key component of cadmium telluride thin-film solar cells, which are among the most efficient and cost-effective photovoltaic technologies currently in large-scale production. Demand for tellurium has risen sharply with the growth of the solar energy industry, and it is now classified as a critical raw material by both the European Union and the United States government. Almost all commercially produced tellurium is recovered as a byproduct of copper refining, from the anode slimes produced during electrolytic refining – primary mining of tellurium is rare.

In 2023 astronomers confirmed the detection of tellurium being created during a neutron star merger – the violent collision of two dead stars that is one of the universe’s primary factories for heavy elements. This placed tellurium firmly among the elements whose cosmic origin has now been directly observed, adding an extraordinary astronomical dimension to a mineral with an already remarkable history.

The most celebrated collector locality for native tellurium is Cripple Creek in Teller County, Colorado, USA, which has produced the finest and most abundant crystallised native tellurium specimens known, including sharp prismatic crystals associated with calaverite, sylvanite, and native gold. The type locality is Faţa Băii (Zlatna) in Alba County, Romania, the site of Müller’s original discovery, where tellurium still occurs in the epithermal gold veins that made Transylvania famous for gold telluride minerals. Kalgoorlie in Western Australia is the other great telluride locality – it was here that in 1893 miners, failing to recognise calaverite as a gold ore, discarded tonnes of it as waste and used it to fill potholes and pave roads; when the gold content was identified in 1896 the resulting second gold rush included the literal mining of the town’s streets. Native tellurium itself is known from Kalgoorlie alongside the tellurides. Other significant localities include Baia de Arieș (Offenbánya) in Romania; the Moctezuma mine in Sonora, Mexico; and the Kochbulak gold deposit in Uzbekistan. No significant occurrences are recorded from the United Kingdom.

Mineralogy

Hazards and Warnings

Toxic element. Tellurium is mildly toxic. Even very small exposures – including inhalation of dust from specimens – can cause tellurium breath, a persistent and penetrating garlic-like odour on the breath and skin that can last for weeks and is caused by the formation of volatile tellurium compounds in the body. Mineral collectors should wash their hands thoroughly after handling specimens and avoid any contact with the mouth or inhalation of dust.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Tellurium
• https://www.mindat.org/min-3906.html
• https://www.handbookofmineralogy.org/pdfs/tellurium.pdf
• https://periodic-table.rsc.org/element/52/tellurium