Thallium was discovered in 1861 by Sir William Crookes (and
independently by Claude-Auguste Lamy a year later) and
occurs in the lithosphere at 0.7 ppm. The name thallium is in
reference to the particularly bright green spectral lines seen in
the spectra resultant from a flame spectroscopy test (from
Greek thallos, meaning a green shoot or twig), the one used in
its discovery. Thallium is a heavy metallic element that exists in
the environment mainly combined with other elements
(primarily oxygen, sulfur, and the halogens) in inorganic
compounds.
