Stunning, 17" Polished Mookaite Jasper Slab - Australia
Radiolarite is a fine-grained, chert-like sedimentary rock that is composed predominantly of the microscopic remains of radiolarians. Radiolaria are tiny (1/10th mm), free-floating, Zooplankton that produce intricate mineral skeletons made of silica. When the radiolarians died their tiny silica based, skeletons settled on the bottom of the ocean and became covered in sediment (mud/clay)
As this sediment turned to sedimentary rock (a process known as diagenesis) the silica from the radiolarian skeletons pinching and coagulates into ribbons, nodules and other irregular concretions. These ribbons, nodules and concretions are the Mookaite within the clay layers. The coloration is due to other (mostly iron based) mineral impurities present along with the silica. So, technically Mookaite could be considered is a fossiliferous, sedimentary rock made out of the tiny skeletons of radiolarians.