The CNO cycle (carbon nitrogen oxygen) alternately called Bethe-Weizsäcker-cycle, is one of two types of fusion reactions by which stars convert hydrogen to helium, the other is the proton proton chain.
Stars that produce most of their energy by the CNO cycle are predominantly those with a mass about 1.3 times the mass of our Sun or greater. Our Sun, and stars comparable in mass or less,...
Its called a cycle because it has to go through steps to form the rocks or minerals. Just like a water cycle is called a water cycle because it also has to go through different stages or steps.