| Although the metal is reasonably abundant in the Earth's crust at a concentration estimated to be about 0.7 mg/kg, mostly
in association with potassium minerals in clays, soils, and granites, it is not generally considered to be commercially recoverable from those forms. The
major source of commercial thallium is the trace amounts found in copper, lead, zinc, and other sulfide ores.
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| Thallium is found in the minerals crookesite TlCu7Se4, hutchinsonite TlPbAs5S9, and lorandite TlAsS2. It also occurs as trace in pyrites and extracted as a by-product of roasting this ore for sulfuric acid production. The
metal can be obtained from the smelting of lead and zinc rich ores. Manganese nodules found on the ocean floor also contain thallium but nodule extraction is prohibitively expensive and potentially environmentally
destructive. In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as sulfide or selenide
complexes with antimony, arsenic, copper, lead, and silver but are rare and have no commercial importance as sources of this element.
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Occurrence