Optical properties of some greenish blue-to-green diamonds

Most green diamonds owe their coloration to radiation exposure that produces the GR]. absorption band. Depending upon the conditions of radiation either a surface color or a bodycolor can result. Natural green diamonds of known geographic origin especially those with a conspicuous bodycolor are extremely rare. A group of seven natural greenish bluetogreen bodycolor type-Ia diamonds from alluvial deposits in Guyana display a distinct but sometimes subtle internal blue-to-green color zoning and a visiblerange absorption spectrum consisting of in addition to the N3 N2 and GR1 bands weak-to-moderate 503 (H3) 496 (H4) and 595 nm bands. We suggest that this combination of features is characteristic of at least one category of natural bodycolor green diamonds. 1.