<P> Cu and Cu have significant applications . Cu is used in Cu - PTSM as a radioactive tracer for positron emission tomography . </P> <P> Copper is produced in massive stars and is present in the Earth's crust in a proportion of about 50 parts per million (ppm). It occurs as native copper, in the copper sulfides chalcopyrite and chalcocite, in the copper carbonates azurite and malachite, and in the copper (I) oxide mineral cuprite . The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US . Native copper is a polycrystal, with the largest single crystal ever described measuring 4.4 × 3.2 × 3.2 cm . </P> <P> Most copper is mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits that contain 0.4 to 1.0% copper . Sites include Chuquicamata in Chile, Bingham Canyon Mine in Utah, United States and El Chino Mine in New Mexico, United States . According to the British Geological Survey in 2005, Chile was the top producer of copper with at least one - third world share followed by the United States, Indonesia and Peru . Copper can also be recovered through the in - situ leach process . Several sites in the state of Arizona are considered prime candidates for this method . The amount of copper in use is increasing and the quantity available is barely sufficient to allow all countries to reach developed world levels of usage . </P> <P> Copper has been in use at least 10,000 years, but more than 95% of all copper ever mined and smelted has been extracted since 1900, and more than half was extracted the last 24 years . As with many natural resources, the total amount of copper on Earth is vast, with around 10 tons in the top kilometer of Earth's crust, which is about 5 million years' worth at the current rate of extraction . However, only a tiny fraction of these reserves is economically viable with present - day prices and technologies . Estimates of copper reserves available for mining vary from 25 years to 60 years, depending on core assumptions such as the growth rate . Recycling is a major source of copper in the modern world . Because of these and other factors, the future of copper production and supply is the subject of much debate, including the concept of peak copper, analogous to peak oil . </P>

What are the uses and properties of copper