Micro-World Gems & Gemology, Fall 2020, Vol. 56, No. 3

Unknown Dendritic Inclusions in Sapphire

Zircon crystals and rutile needles (left) and dendritic inclusions (right) in sapphire.
Left: When the pinkish purple sapphire was viewed under darkfield illumination, the only inclusions visible underneath the table were zircon crystals and rutile needles. Right: Examining the same area with fiber-optic light revealed unknown dendritic inclusions. Photomicrographs by Ezgi Kiyak; field of view 2.90 mm.

The authors recently examined a 4.03 ct light pinkish purple unheated sapphire. When viewed under darkfield illumination, the inclusion scene at first seemed fairly vacant and occupied only by sparse zircon crystals and rutile needles (see above, left). However, microscopic observation with fiber-optic light revealed large, delicate dendritic inclusions underneath the table (see above, right) that resembled a fern frond. The dendritic inclusions seemed to be flat and parallel to each other and extended the entire length of the table. Small round platelets were associated with the “branches” of the inclusions.

Further examination with a polariscope and conoscope helped prove that the dendritic inclusions were oriented parallel to the basal plane of the host corundum. A distinct uniaxial interference pattern was observed when viewing these inclusions from a perpendicular angle. The thinness and relative distance to the surface of the stone made it difficult to identify the inclusions with Raman spectroscopy. This is the first example of such dendritic inclusions in sapphire the authors have observed. However, a similar inclusion has been observed previously in a heat-treated blue sapphire (see Spring 2007 Lab Notes, pp. 54–55).

Ezgi Kiyak is gemologist trainee, and Augusto Castillo is senior staff gemologist, at GIA in New York.