Various places....
Ag Behenate - Huang, Toraya, Blanton & Wu, 1993 (58.380)
Silicon - 2010 CODATA (5.4310205, Diamond FCC)
Cr2O3 - NIST SRM 674 [4.95916(12), 13.5972(6)] trigonal - hexagonal scalenohedral
CeO2 - NIST SRM 674 (5.41129, FCC)
LaB6 - NIST SRM 660a (4.1569162, Cubic)