  Carbonado-diamond is the most enigmatic of diamond types, and surprisingly
there are few optical studies. In some cases, the diamond peak at 1332.5 cm-1
is absent, and the presence of a D-band graphite peak around 1320 cm-1 is
observed in our Raman investigation. The disappearance of the diamond peak in
carbonado-diamond is interpreted as the combined effect of small crystal size
and the high absorption of graphite. The photoluminescence spectra of
carbonado-diamond shows two new zero phonon lines at 584.2 nm (2.12 eV) and at
743 nm (1.67 eV). By heating the carbonado-diamond to 1500 oC for ten minutes
in argon the appearance of an additional peak at 693.5 nm (1.786 eV) is
detected. The infrared absorption spectra of carbonado-diamond powder indicate
either extremely low or extremely high absorption.
