Estonian oil shale

The rock burns because it is made of fossil algae.

Kukersite is the Estonian oil shale that matters, a Middle Ordovician rock whose organic matter is considered entirely marine in origin and consists almost wholly of telalginite derived from a colonial microorganism called Gloeocapsomorpha prisca. Its kerogen runs about 76 to 77.5 per cent carbon and 9.4 to 9.9 per cent hydrogen, with a hydrogen to carbon ratio of 1.48, which plots it as a Type II kerogen. The major components are phenolic units with linear alkyl side chains.

There are actually two shales here and only one of them is used. The Baltic Basin holds the Middle Ordovician kukersite, worked in the Estonian and St Petersburg fields, and the Lower Ordovician Dictyonema shale. The Dictyonema covers about 11,000 square kilometres of northern and north-western Estonia at depths of 10 to 90 metres in seams 1 to 8 metres thick, and its reserves considerably exceed those of kukersite. It is the quality that keeps it in the ground.

The seam thins as you go south. The productive bed runs 2.7 to 3.0 metres thick in the northern part of the deposit and narrows to 1.4 to 2.0 metres in the south and west. The Tapa deposit, lying southwest, sits 60 to 170 metres below the surface and reaches 2.0 to 2.3 metres at its thickest, and it is not being worked. Between them the two main deposits cover roughly 5,000 square kilometres.

The industry is as old as the country. The Estonian deposits were first developed in the 1920s, after the state achieved independence, and by 1939 about 1.7 million tonnes a year were being processed.

This is a live industrial landscape rather than a collecting site, and the Tallinn University of Technology runs a dedicated oil shale competence centre around it. What you can take away is the idea: a rock that is, quite literally, compressed pond scum from the Ordovician, and which ran a country's electricity.