HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California Cady, S. L. ; Wenk, H. R. ; Downing, K. H. Abstract Publication: American Mineralogist Pub Date: December 1996 DOI: 10.2138/am-1996-11-1211 Bibcode: 1996AmMin..81.1380C