Thallium

In nature, thallium is found in the Earth's crust, 0.7 ppm, in minerals such as crookesite, lorandite and hutchinsonite [6]. The isotopes found in nature are ²⁰³Th (29.50 %, stable) and ²⁰⁵Th (70.50 %, stable) [6].

In pure solid form, thallium exist in a hexagonal close-packed structure [3].