Koroit Opal is found whithin Ironstone a type of sedimentary rock. The ironstone matrix supports and surrounds the Opal adding to its unique character. Over millions of years silica rich waters seep into voids and fissures ,the silica then solidifies forming microscopic silica spheres which make up the Opal. Fissures that form in Koroit are natural cracks or fractures where the opal forms.these fissures can vary in size & depth and often play a significant role in the Opals appearance and value . The fissures form as a result of Geological processes including the movement of tectonic plates and the natural expansion of the rock due to temperature changes ,fissures can create unique patterns & enhance the play of colour in the Opals.They often appear as thin jagged lines or thicker cracks that can be filled with opal or other minerals, Opals with well defined fissures can be more aesthetically pleasing and can be more valuable as they add to the stones uniqueness & visual appeal