This huge size 18 carat unheated sapphire from Tigray in Northern Ethiopia shows a highly unusual type of golden silk. Usually silk in unheated sapphire is whitish in color and is composed of rutile a.k.a. titanium dioxide.
This particular item is likely to have higher concentrations of hematite and ilmenite which is generally the most frequent companion minerals seen in golden silk. Usually seen in golden and black star sapphires from both Thailand and Kenya, seeing these golden threads suspended in a relatively clean blue sapphire crystal is rare.1