Bicolor Rough Diamond Crystals
The GIA laboratory in Antwerp regularly receives pink diamond crystals for examination as part of the Diamond Origin Report. This recent service has allowed GIA researchers to study a greater number of rough diamonds in addition to their faceted counterparts. Two crystals, weighing 1.75 and 1.44 ct and both reportedly from Australia, were among those submitted. These were considered quite interesting, as they contained colorless and pink sections with distinct boundaries.
The color in the vast majority of naturally pink diamonds is attributed to a broad absorption band at about 550 nm within the visible absorption spectrum. This band generally results from distortion of the crystal lattice from plastic deformation due to stress after crystal growth. However, much remains unknown about the actual formation and configuration of this feature. Therefore, these two crystals provide a unique chance to study natural diamond formation and the origin of pink color in greater detail.
The pink section of both analyzed samples likely experienced great stress in order to undergo the plastic deformation necessary to impart the pink color. The colorless sections were not similarly deformed so presumably they represent a different and later growth event.