File:Kukersite (Viivikonna Formation, Middle Ordovician; Kohtla-Järve, Estonia).jpg

English: Kukersite from the Ordovician of Estonia.

The brown material is kukersite, a variety of oil shale (although lithologically, this is not oil shale). Kukersite is a hydrocarbon-rich sedimentary rock that burns in a fire. Upon heating, kukersite will release petroleum. The whitish structures in the rock are fossil bryozoans ("moss animals"), a group of sessile, benthic, filter-feeding, colonial lophophorates that make calcareous skeletons. Bryozoans were abundant in Paleozoic oceans.

Kukersite is generally referred to as an oil shale, but has also been characterized as a type of torbanite, which is a "sapropelic coal" rich in alginite phytoclasts. In the case of Estonian kukersite, the alginite phytoclasts are the fossil remains of Gloeocapsomorpha, an organic-walled cyanobacterium similar to modern Gloeocapsa, a freshwater cyanobacterium. Gloeocapsomorpha is often incorrectly called "algae". Under ultraviolet black light, Gloeocapsomorpha fluoresces. In addition to the Baltics area, this type of organic-walled microfossil is common in the Ordovician of North America and Australia - all three landmasses were in tropical to subtropical settings at the time. Gloeocapsomorpha was hit hard by the end-Ordovician mass extinction, which was caused by an Ice Age and a global sea level drop (regression), but it may have persisted into the Devonian.

Kukersite has economic significance - in Estonia, it is mined and burned in power plants to make electricity.

Stratigraphy: "Estonia Deposit", Kiviõli Member, Viivikonna Formation, Kukruse Stage, Middle Ordovician (sensu traditio)

Locality: unrecorded/undisclosed site at or near the town of Kohtla-Järve, northeastern Estonia

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See info. at: en.wikipedia.org/wiki/Kukersite and

en.wikipedia.org/wiki/Oil_shale_in_Estonia