The gemological properties of the material as quoted from their promotional literature "Autheticity Certificate " are:
Material: Tempered Itryium Oxide
Hardness: 8.77 Mohs
Specific Weight 5.72
Using a linearly calibrated (Using Synthetic Spinel and Diamond) and specially modified dual range reflecting refractometer (The Jemeter Digital 90) we measured a refractive index of approximately 2.2x. The near colorless stone was singlely refractive. The stone was inert to long wave ultraviolet but had a weak greenish yellow short wave ultraviolet response. Based on a ratio calculation to diamond (we did not do a hydrostatic SG) the SG was approximately 1.70 times as dense as diamond for an SG of approximately 5.9x. Thermal conductivity tests as a simulant. The stone is not electrically conductive. The Presidium Dual Tester read 058, which is in the CZ range. These properties were consistant with the tabulated properties of cubic zirconia (CZ). They were not consistant with published data on Yttrium oxide (Yttrolox).
From our memory of previous experiments we had
run on Cubic Zirconia, we searched our collection of colorless material
and came up with 3 samples (out of 37) which showed a "rare earth" type
of spectra, presumally due to trace amounts of some unknown "rare earth".
Two of these samples showed what we considered as IDENTICAL spectra to
the "Van Graff Diamond", using both Vis-NiR and Photoluminescence spectroscopy.
One of the three CZ's showed a dissimilar "rare earth" spectra, and is
shown below for comparison.
Visible - Near InfraRed Spectroscopy
SAS2000 LNIS (Liquid Nitrogen
Another CZ With Rare Earth Spectra
It appears to us that the "Van Graff Diamond" is nothing more than a Yttrium stabilized Cubic Zirconia !