Graphite in Sapphire
The gem deposits of Sri Lanka are known to contain graphite, which sometimes appears as inclusions in the sapphires Sri Lanka is famous for. We recently examined one such sapphire: a transparent to translucent, light brownish gray, waterworn single crystal section, with one polished window perpendicular to the optic-axis direction.
Weighing 4.94 ct and measuring 8.75 × 7.35 × 5.80 mm, the sapphire was purchased from Sajith Masilamani in Ratnapura, Sri Lanka. It was said to be from the Ratnapura District in Sabaragamuwa Province.
Under the microscope, the stone’s inclusion scene proved quite interesting. On display was a large primary three-phase fluid inclusion containing water, liquid, and gaseous carbon dioxide, together with graphite as the solid phase. Of particular interest, as shown in the figure above, were loose graphite plates that moved freely in the confines of the fluid inclusion chamber.
In addition to the mobile graphite plates, the inclusion was quite active and appeared to “boil” while it homogenized under microscopic examination. A somewhat similar inclusion in a Sri Lankan sapphire is shown in Photoatlas of Inclusions in Gemstones, Volume 3 (E.J. Gübelin and J.I. Koivula, 2005, Opinio Publishers, Basel, Switzerland, p. 280). Therefore, this particular inclusion with mobile graphite was unusual but not unique.
