petrogenesis
noun
pet·ro·gen·e·sis ˌpe-trō-ˈje-nə-səs 
: the origin or formation of rocks
petrogenetic
ˌpe-trō-jə-ˈne-tik
adjective 
Word History
Etymology
borrowed from German Petrogenese or Petrogenesis, from petro- petro- + -genese, -genesis genesis
First Known Use
1886, in the meaning defined above