Lab Notes Gems & Gemology, Spring 2013, Vol. 49, No. 1

Orange Diamond with Unusual Color Origin

Orange Diamond Unusual Color Origin
Figure 1. This 1.53 ct diamond was color graded as Fancy Intense pinkish orange. Spectroscopic analysis revealed it was type IIa and dominated by an approximately 550 nm band absorption, which usually introduces a pink-red color in natural diamonds rather than orange. Photo by Jian Xin (Jae) Liao.
Orange bodycolor in diamond is usually caused by an absorption band centered at approximately 480 nm or by a high concentration of isolated nitrogen. Meanwhile, it is well known that the 550 nm absorption band often introduces pink to red colors. Physical models of these two optical centers have not been resolved yet. The New York laboratory recently examined an orange diamond whose color was attributed mainly to the 550 nm absorption band.

This 1.53 ct heart-shaped diamond (6.84 × 7.76 × 3.88 mm) was color graded as Fancy Intense pinkish orange (figure 1). Color was distributed evenly throughout the stone, which was very clean and showed no internal features under the microscope. The absorption spectrum in the infrared region revealed that it was a regular type IIa diamond, with no nitrogen-or hydrogen-related absorptions. The UV-Vis region showed a broad absorption band centered at ~550 nm and its corresponding band at ~390 nm, absorption features typical of natural type IIa pink diamonds. From the optical centers detected, we would not expect this diamond to show a dominant orange bodycolor.

The reason for this discrepancy is not fully understood. Our finding from this stone demonstrates the complexity of diamond color origin.