corundum, Cambodia.12, Vietnam.12, gems

While trapiche emerald is well known, trapiche corundum (especially blue sapphire) is considerably rarer. The authors examined 33 blue sapphires from Vietnam and 27 from Cambodia. The majority showed trapiche structure, but non-trapiche specimens were included for comparison. The trapiche sapphires typically featured a brown core and brown to yellowish brown arms separating the sections of blue crystal; dotted and needle-like inclusions were also seen. Iron and titanium were both present in the samples, but the iron was concentrated in the trapiche core while the titanium was evenly distributed for the most part. The authors also compared the visual characteristics of trapiche rubies and sapphires, as well as trapiche vs. star phenomena. The trapiche structure could point to a multi-stage growth process that starts at the core, with the arms and blue crystal segments growing concurrently but at different rates.