Zinc makes up about 75 ppm (0.0075%) of the Earth's crust, making it the 24th most abundant element there. Soil contains 5–770 ppm of zinc with an average of 64 ppm. Seawater has only 30 ppb zinc and the atmosphere contains 0.1–4 µg/m3.
The element is normally found in association with other base metals such as copper and lead in ores.Zinc is a chalcophile ("sulfur loving"), meaning the element has a low affinity for oxygen and prefers to bond with sulfur in highly insoluble sulfides. Chalcophiles formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, which is a form of zinc sulfide, is the most heavily mined zinc-containing ore because its concentrate contains 60–62% zinc.
Other minerals, from which zinc is extracted, include smithsonite (zinc carbonate), hemimorphite (zinc silicate),wurtzite (another zinc sulfide), and sometimes hydrozincite (basic zinc carbonate). With the exception of wurtzite, all these other minerals were formed as a result of weathering processes on the primordial zinc sulfides.
World zinc resources total about 1.8 gigatonnes. Nearly 200 megatonnes were economically viable in 2008; adding marginally economic and subeconomic reserves to that number, a total reserve base of 500 megatonnes has been identified. Large deposits are in Australia, Canada and the United States with the largest reserves in Iran. At the current rate of consumption, these reserves are estimated to be depleted sometime between 2027 and 2055. About 346 megatonnes have been extracted throughout history to 2002, and one estimate found that about 109 megatonnes of that remains in use.
Five isotopes of zinc occur in nature. 64Zn is the most abundant isotope (48.63% natural abundance).This isotope has such a long half-life, at 4.3×1018 a, that its radioactivity can be ignored.Similarly, 70Zn (0.6%), with a half life of 1.3×1016 a is not usually considered to be radioactive. The other isotopes found in nature are 66Zn (28%), 67Zn (4%) and 68Zn (19%).
Several dozen radioisotopes have been characterized. 65Zn, which has a half-life of 243.66 days, is the most long-lived isotope, followed by 72Zn with a half-life of 46.5 hours. Zinc has 10 nuclear isomers.69mZn has the longest half-life, 13.76 h. The superscript m indicates a metastable isotope. The nucleus of a metastable isotope is in an excited state and will return to the ground state by emitting aphoton in the form of a gamma ray. 61Zn has three excited states and 73Zn has two. The isotopes65Zn, 71Zn, 77Zn and 78Zn each have only one excited state.
- n30Zn + e⁻ → n29Cu