Kukruse oil shale (after the village of Kuckers [Kukruse], Estonian SSR), a variety of combustible shale found in Middle Ordovician deposits in the Baltic shale basin.
Kuckersite is a marlaceous yellowish-brown rock enriched with organic matter; it contains 20–70 percent kerogen (an organic substance formed by the biochemical transformation of blue-green algae), 25–40 percent calcium carbonate, and arenaceo-argillaceous material. The ash content of the various strata ranges from 40 to 60 percent (for dry fuel), and the sulfur content, 1.1–1.8 percent. The heat of combustion is 11.6 megajoules per kg (3,500 kilocalories per kg).
Kuckersite occurs in thin (0.03–0.6 m) layers separated by interlayers of marl and limestone; these combine to form an industrial bed with an aggregate thickness to 5 m. A working batch comprises 4–6 layers of kuckersite with an aggregate thickness of 0.7–2.0 m. Kuckersite is used primarily as a power fuel. It is also used in the manufacture of household gas, liquid fuel, and chemical products. The ash is used in the manufacture of various building materials and for liming soil.