Pink Sapphire with Graphite Inclusion
Graphite inclusions in corundum can occur as minute bodies inside negative crystals alongside trapped diaspore and carbon dioxide. They can also appear as separate large metallic-looking hexagonal plates or jumbled clusters of small flaky crystals. Graphite in sapphire commonly occurs in those from Sri Lanka or Batakundi, Pakistan (V. Pardieu et al., “Sapphires reportedly from Batakundi/Basil area,” GIA Research News, May 12, 2009). The author recently found a surprisingly well-formed hexagonal graphite platelet with surface etchings in a pink sapphire from Sri Lanka (see above). Taking into account the luster and structure of the inclusion in this particular stone, it was identified as graphite under the microscope.
Graphite is a stable form of layered carbon occurring as a submetallic opaque mineral with a black to steel-gray color range. It typically forms in carbon-rich metamorphic rock or in pegmatite. Formation of this inclusion is dependent on the grade of metamorphism and temperature in the growth environment. It is rare to find such a clean example of a singular graphite inclusion demonstrating the crystal system it belongs to. This graphite inclusion in pink sapphire was a remarkably pristine example of this inclusion and host relationship.
