Optical Spectra of Spinel, MgAl2O4       (gahnite below)

1930s

1950s
1960s
1970s 1980s
1990s
2000s 2010s
2020s

Optical Spectra of Gahnite, ZnAl2O4

1980s
1990s
2000's
2010s 2020s