I picked up this pure black corundum stone in about 2010 in a fossicking trip to Tomahawk Creek in the Central Queensland gemfields. ( 7.17mm x 4.5mm x 3.36 high). I kept it as it had a sliver of deep blue sapphire that throws a shaft of blue light. I cut and polished it myself to retain as much of the inclusion as possible, resulting in a very deep stone that will be challenging to mount securely, but worth it. It's quite difficult to photograph to show the inclusion, but the photos under torchlight clearly show the the narrow bar of blue sapphire running the length of the stone. This results a polished black stone that catches the eye with a flash of blue light in sunlight or other strong light.