gems, corundum, Tanzania.12, spinel, tanzanite, zoisite, Merelani, Mahenge, Tunduru

In a parcel of over thirty rubies from Myanmar’s Mong Hsu mines, all of the stones contained zoned clouds of cottony ‘silk’, believed to be diaspore, as seen in the sample shown in Figure 1. However, this stone stood out from the rest of the lot. In addition to the wispy diaspore silk, it also contained several bands of fine, intact silk needles, likely rutile (Figure 2). It was, in fact, the only stone in this suite to contain this type of silk. While rutile silk needles are uncommon in Mong Hsu rubies, they have been reported on rare occasions, and we have also observed them in a few samples from our laboratory’s reference collection. It is worth noting that despite the intact silk needles, this stone was determined to have been heated. Supporting evidence included other inclusions, such as melted fingerprints, as well as a clear 3309 series with 3232 in the infrared spectrum and zoned chalky short-wave ultraviolet fluorescence. This serves as an important reminder that the presence of intact silk needles does not always indicate that a stone is unheated.