Sources of Thallium:  Thallium is found in iron pyrites and in crookesite, hutchinsonite and lorandite.

                                    It is recovered from the byproducts of lead and zinc refining as well as from the

                                    flue dusts from roasting certain sulfide ores, mainly pyrites. Thallium is found naturally

                                    in the Earth's crust as well, though in the small ratio of 530 ppb by weight, and in

                                    the Ocean, in the ratio of 0.001 ppb by weight.