1. How many kinds of copper atom are there?
Copper is an element, which means chemistry cannot split it into simpler materials. Its symbol is Cu and its atomic number is 29, so every copper atom has 29 protons. Nature makes copper atoms in two stable versions, called isotopes. They have the same number of protons but different numbers of neutrons: copper-63 has 34 and copper-65 has 36.
The U.S. National Institute of Standards and Technology lists their shares in ordinary copper as about 69.15% copper-63 and 30.85% copper-65 [1]. Put simply, if you could pick ten copper atoms at random, about seven would be copper-63 and about three would be copper-65. They behave almost the same, because chemistry mostly depends on the protons and electrons, not the neutrons.
"Two kinds" refers only to atoms that last. Unstable, radioactive versions of copper can be made in laboratories, and a radioactive nickel atom will matter in section 3. First, the bigger question: how are copper atoms made?
2. Inside what kind of star were copper atoms made?
The lightest elements came from the early universe and from stars fusing small nuclei together. Many elements heavier than iron are built by a different trick: an atomic nucleus catches a neutron, becomes slightly heavier, and sometimes changes into the next element up. If neutrons arrive slowly, the nucleus has time to settle between catches. This is called the slow neutron-capture process, or s-process.
A 2020 study measured copper in 56 red giant stars in the central bulge of the Milky Way. In stars with the least iron, copper falls off too, as you would expect from a "secondary" element, one whose production depends on heavier "seed" nuclei supplied by earlier stars. The authors read this as a sign that copper is made by the weak s-process, which runs in the helium-burning and later stages of massive stars [2]. (A simple way to picture "secondary" is baking with leftovers: the more a star starts with, the more copper it can make.)
This is not a settled textbook fact. For years, astronomers argued over whether most copper comes from massive stars or from a different kind of exploding star, a type Ia supernova. A 2007 paper built models of how element amounts change over time in two places, a star cluster called Omega Centauri and the Milky Way's disc. It concluded that massive stars are the major source in both [3]. So the careful statement is: the evidence points to massive stars, and the details are still being tested.
3. Is the story of how copper is made still being corrected?
Yes, and one example shows how. To predict how much copper-63 a massive star makes, scientists need to know how likely unstable nickel-63 is to catch a neutron along the way. Nickel-63 is hard to study because it is radioactive. In 2013 a team at the n_TOF neutron facility at CERN measured this for the first time [4].
The new numbers mattered. In a computer model of a star 25 times the mass of the Sun, they had a significant effect on how much copper-63, and a few neighboring atoms, the slow process produced. The authors say this allows tighter limits on how much copper is made later, when such a star explodes as a supernova [4]. Even this measurement carries an uncertainty of around 20%, so the full recipe is still being refined.
4. Why is the copper in the ground not shiny copper?
Once star material gathered into Earth, copper ended up in rocks. A little copper does appear as pure metal; the U.S. Geological Survey notes that copper is one of the few metals found in its pure state in nature. But copper also attaches strongly to sulfur, and it forms many sulfide minerals [5]. A well-known one is chalcopyrite, with the chemical formula CuFeS2 [5].
The formula says each unit has one copper atom, one iron atom and two sulfur atoms, so one atom in four is copper. By mass the share is about 35%: copper's atomic weight is about 63.5 and the whole unit is about 183.5 (our own quick calculation from standard atomic weights, not a figure quoted from the sources). The copper in chalcopyrite is chemically combined, so it has to be separated out before it becomes the metal in a wire.
Copper is also spread thinly through ordinary rock. The USGS estimates the average in the upper continental crust at 27 milligrams per kilogram, which is about 27 grams in a tonne of rock [5]. Mines work where nature has gathered far more than that into one place.
5. How can you keep exploring where copper comes from?
Look for a copper-colored object you already know is safe to handle, such as an old coin, and tell the whole story in one minute: two kinds of atom, built in heavy stars, later found in minerals like chalcopyrite. Notice where you say "scientists think." That gap is where the research is.
If you want the originals, the abstracts of the 2020 copper study (arXiv:2007.00397) and the 2013 nickel-63 paper (arXiv:1304.3310) are free online. A question to take with you: if copper needs seed nuclei from earlier stars, what does that say about how old the atoms in a wire are?