Thanks for the observation. The spot is black and under the microscope in a dark field looks like a tiny piece of rock with sharp crystalline structure. The crystalline structure of the ruby is very fine without evidence of heat although I detected a small vein of wax behind the spot. Possibly to hide a fissure there but is nothing on the crown. However, as I only paid $50 a ct and it tests as ruby. I am not too worried about it’s origin or treatment. It is worth knowing that I collect lame and flawed gemstones no one else wants because they are cheap and infinitely more interesting under a microscope than the boring, perfectly clear top quality ones that hit the headlines and the jewelry stores.
Note that my wife and I are both on the lookout for the unusual, rare and interesting ones. To date we have over 1500 eclectic examples no self respecting jeweler would ever cintemplate for a mount.