Black onyx is a form of agate, or chalecedony quartz, which naturally forms in concentric layers in a variety of colors. Onyx is created in crevices and cavities by the cooling of molten volcanic rock.
8mm has 2.5mm hole. 10mm, 12mm and 14mm have 3.0mm hole
*Photos below show 10, 12, & 14mm black onyx fireballs on omega necklace with 8 & 10mm silver rondelles w/clear crystals.