The El Teniente mine works on a porphyry copper deposit, ca. 50km E of Rancagua. Core or plug of an extinct volcano. Known for its very large gypsum crystals, including one measuring l0ft.x3 in. (3 meters x 8 cm.)
Refs.: Palache, C., Berman, H. & Frondel, C. (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, 7th. edition, Volume I: 196, 222.
Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 1010.
