minerals Article A Defect Study and Classification of Brown Diamonds with Deformation-Related Color Thomas Hainschwang 1,*, Franck Notari 2 and Gianna Pamies 1 1 GGTL Laboratories, Gnetsch 42, 9496 Balzers, Liechtenstein;
[email protected] 2 GGTL Laboratories, 2 bis route des Jeunes, 1227 Geneva, Switzerland;
[email protected] * Correspondence:
[email protected]; Tel.: +423-262-24-64 Received: 3 September 2020; Accepted: 7 October 2020; Published: 12 October 2020 Abstract: For this study, the properties of a large sample of various types of brown diamonds with a deformation-related (referred to as “DR” in this work) color were studied to properly characterize and classify such diamonds, and to compare them to pink to purple to red diamonds. The acquisition of low temperature NIR spectra for a large range of brown diamonds and photoexcitation studies combined with various treatment experiments have opened new windows into certain defect characteristics of brown diamonds, such as the amber centers and naturally occurring H1b and H1c centers. It was determined that the amber centers (referred to as “AC” in this work) exhibit rather variable behaviors to annealing and photoexcitation; the annealing temperature of these defects were determined to 1 range from 1150 to >1850 ◦C and it was found that the 4063 cm− AC was the precursor defect of many other ACs. It is suggested that the amber centers in diamonds that contain at least some C centers are essentially identical to the ones seen in diamonds without C centers, but that they likely have a negative charge.