Radiolarite is a siliceous

Siliceous ooze

Siliceous ooze is a soft siliceous pelagic sediment that covers large areas of the deep ocean floor. Siliceous oozes consist predominately of either diatoms or radiolarians. Sometimes, it contains lessor proportions of sponge spicules or silicoflagellates. Diatoms are golden-brown algae that...

, comparatively hard, fine-grained, chert

Chert

Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...

-like, and homogeneous sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 that is composed predominantly of the microscopic remains of radiolarians. This term is also used for indurated radiolarian oozes and sometimes as a synonym of radiolarian earth. However, radiolarian earth is typically regraded by Earth scientists to be the unconsolidated equivalent of a radiolarite. A radiolarian chert is well-bedded, microcrystalline radiolarite that has a well-developed siliceous cement or groundmass.

The Windalia radiolarite is a Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 formation in Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

. The formation contains abundant foraminifera

Foraminifera

The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...

, radiolaria and calcareous

Calcareous

Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...

 nanoplankton fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s. Locally the varicolored opal

Opal

Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...

ine to chalcedonic

Chalcedony

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of the minerals quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic...

 radiolarite is mined and used as an ornamental stone termed mookaite.

External links

• http://www.nps.gov/goga/forteachers/upload/Rock%20information%20cards%20TT_small.pdfRadiolarian Ribbon Chert in the Marin Headlands
  Marin Headlands
  The Marin Headlands is a hilly area at the southernmost end of Marin County, California, just north of the Golden Gate Bridge. The Headlands are located just north of San Francisco, immediately across the Golden Gate Bridge. The entire area is part of the Golden Gate National Recreation Area...
  
  (NPS)]
• Chert FAQ - NPS
• Photo of radiolarite in Corsica, France (text in French) retrieved 2009-05-17