Tellurium (Te) is a relatively rare, brittle, and silver-white metalloid with a crystalline structure. It is found naturally in the Earth's crust and is primarily obtained as a byproduct of the refining of copper ores. Tellurium has the unique property of being more conductive in certain directions, which can be valuable in specific electronic applications. Its compounds, especially with metals like cadmium (CdTe), are used in semiconductors and solar cells. Moreover, binary alloys of tellurium with bismuth, lead, and other metals have been studied for their thermoelectric properties, which can convert heat directly into electricity. The photoconductivity of tellurium also makes it valuable in some photovoltaic applications. Another noteworthy application of tellurium is in the rewritable optical discs (DVD-RW, Blu-ray), where it's used in the form of an alloy with antimony.