Palke and Breeding (2017) claim that rutile needles with shape-preferred orientation included in gem corundum result from epitaxy of rutile on the corundum surface during growth of corundum in a magmatic environment. This is in contrast to the presently accepted view of oriented rutile needles in corundum being products of exsolution during cooling.

While confirming that Ti dissolves into gem corundum and precipitates as rutile needles to obtain star sapphire, and that both processes are common practice in the heat treatment of ruby and sapphire at high temperatures (1800–1100 °C; e.g., Schmetzer et al. 2015), Palke and Breeding (2017)...

You do not currently have access to this article.