It is a rare metal, with an abundance similar to that of silver. It is generally found in deposits with zinc and refineries which produce this more common metal often sell indium as well. It is corrosion resistant. Like pure tin, pure indium emits a squealing sound when bent. Although in appearance thallium resembles lead, it does not have the corrosion resistance of lead and so has few commercial applications.
Thallium compounds are quite toxic and some have been used as rat poisons.
A few compounds are used in glasses for special infra-red lenses. Background links go to the Periodic Table created at Los Alamos National Laboratories by Robert Husted.