Australian Black Sapphire, oval cabochon.
This is a genuine Corundum Sapphire gemstone, note the characteristic play of “silk” across the gemstone surface in the image. This “silk” consists of countless Rutile rod inclusions lined up in straight lines, so densely arrayed as to render the gemstone quite opaque; light penetrating is instantly refracted back, creating a “Star” across the gemstone surface. Though the startling effect is not captured in the images, this gemstone has been cut to bring out this six-point “Star”, or “Asterism”, especially under pin-point light or direct sunlight, and this asterism is permanent. It is a “Star Sapphire”
10mm width across the top, 4.5mm at rear and 1.9mm thick, a strong durable ring. And the Black Star Sapphire itself is very durable, being of the extremely tough Corundum, the second toughest crystal gemstone after Diamond, and being cut cabochon, having no facets to knock and nick.