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

Staurolite in a Mozambique Ruby

Staurolite crystals surround a negative crystal.
Orangy red staurolite crystals surround a negative crystal in a Mozambique ruby. Planes of thin films can be seen behind them. Photomicrograph by Nicole Ahline; field of view 1.42 mm.

Rubies from Mozambique have a well-known inclusion suite that can consist of particle clouds, planes of platelets, and negative crystals as well as sulfite and amphibole crystals. These inclusions and their trace element chemistry make the geographical origin of Mozambique rubies less difficult to decipher. Recently, a 1.11 ct unheated ruby was examined by the author for identification. Internally there were scattered silk with planes of thin films as well as negative crystals. These inclusions plus trace element chemistry collected by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses confirmed the stone to be from Mozambique.

Mozambique rubies have a consistent suite of inclusions, and noting something out of the ordinary is quite uncommon. Alongside the negative crystals were clusters of a transparent orangy red crystal that the author had no prior knowledge of seeing in a Mozambique ruby (see above). Raman spectroscopy identified the unknown crystals as staurolite, a nesosilicate mineral known to occur in Mozambique. In a recent issue of G&G, staurolite was examined and documented for the first time as an inclusion in corundum, specifically in a Madagascar ruby (Spring 2020 Micro-World, pp. 144–145). The author believes that this staurolite is the first of its kind documented in a Mozambique ruby. Inclusions such as these will forever keep gemologists on the lookout for the next unknown.

Nicole Ahline is senior staff gemologist at GIA in Carlsbad, California.

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