Mookaite is actually a fossilifzed ferous sedimentary rock. The correct geological term for the formation that Mookaite occurs in is " Windalia Radiolarite." This stunning multi-colored stone is found in the Kennedy Ranges near Gascoyne Junction, which is about 100 miles inland from the coastal town of Carnarvon, in Western Australia. Perth, the capital of Western Australia, is about 600 miles to the south. 
The "Windalia Radiolarite" consists of varicolored radiolarian commonly occuring in outcrops. Associated with the Mookaite in many locations are imprints of Ammonites. Stratigraphic relationships with adjacent areas, indicate that the "Windalia Radiolarite" formed originally on a marine shelf. Microscopic examination of the radiolarite has shown that this rock consists principally of the remains of tiny organisms known as 'radiolaria', which possessed an unusual skeletal structure of opaline silica. Countless numbers of these microscopic animals were deposited as sediment in the shallow waters, near shore area of ancient seas. When the seas retreated, these sediments were cemented into solid rock by silica carried in groundwater, either from the radiolaria themselves or from weathered rocks nearby.
The name "Mookaite" is derived from the locality where the rock is found, namely 'Mooka Creek'. According to local Aboriginaes, "mooka" means "running waters", no doubt in reference to the many fresh water springs that feed Mooka Creek in the rainy season.
Mookaite is many times incorrectly called mookite, mookalite, mookerite, mook, mook jasper, moukaite, moakite, moukalite or mouakite.
Mookaite can be correctly described as Chert, Opalite, Chalcedony or a combinations of two or of all three. The amount of silica in the material determines its physical description. This creates difficulties when digging Mookaite as the more Opaline in the rock, the more brittle it becomes. In this form, it is useless for cutting, as the lightest hit will cause it to fracture. The best material is the Chalcedonic variety. It generally occurs as nodules, large and small, lying in decomposed radiolarian clay beneath the floor of Mooka Creek. It appears that the silica rich and mineralised solutions have seeped through the radiolarite beneath the floor of the usually dry Mooka Creek bed.
These solutions have concentrated in various locations and collected as nodules and sheets of the multi-colored Chalcedony variety, or better yet, gem quality Mookaite. Subsequently, the radiolarite with less silica has decomposed into beds of soft white clay which now surround the stunning nodules. Unfortunately there is a fair degree of underground water lying and running through these clay beds which make it extremely messy and difficult to dig out the good Mookaite from under the dry creek bed. 
