Tellurium - a surprisingly rare element

Tellurium - a surprisingly rare element

Tellurium is one of the rare instances, where finding a pure sample is much more likely than any of the compounds. It belongs to the least abundant stable elements in the Earth's crust, with rarity comparable to these of platinum group metals or gold. It is however not a metal, but a metalloid with properties similiar to these of selenium (Se) or sulfur (S) of the same group - chalcogens.

Pure tellurium in a jar.

Tellurium in it's pure form is silvery white, but over time, especially when finely divided, it might develop a thin layer of surface oxidation that causes it to take different colors, as observed on some of the more reactive transition metals. It's also surprisingly dense - with the density of 6,24 g/cm3, for a given volume it's heavier than titanium, vanadium, gallium and many other metals.

Pure tellurium chunk.

As typically observed in metalloids, Te is also extremely brittle. So brittle in fact, that just picking it up with a pair of tweezers and placing it to take a photo, caused all the crumbles visible above to separate from the chunk. For that reason, any glass bottle or ampoule that tellurium is kept in will quickly get coated with a layer of microscopic dust and lose it's clarity. 

Brittleness of tellurium gets even more annoying when you learn how toxic and problematic it is when it enters a human's body - even in relatively small amounts, tellurium compounds are able to make a person smell terribly for a long time. It is also able to be absorbed through the skin, so it's best to avoid handling it bare handed at all.

Coming back to what was mentioned in the first paragraph, compounds of tellurium exist in nature primarily in the form of metal tellurides, with the most well known being gold telluride calaverite and gold-silver telluride sylvanite. These minerals are rather expensive from a collector's perspective, especially compared to pure, plain metalloid form.

As a fun fact, metal tellurides, like CdTe, are used in production of photovoltaic cells and infrared radiation detectors. Most of the naturally existing Te is also composed of technically radioactive isotopes, however their half-life is long enough to be considered stable.