Torbanite, also known historically as boghead coal or kerosene shale, is a variety of fine-grained black
oil shale. It usually occurs as
lenticular masses, often associated with deposits of Permian
coals.[1][2] Torbanite is classified as
lacustrine type oil shale.[3] A similar mineral,
cannel coal, is classified as being a terrestrial form of oil shale, not a lacustrine type.[3]
Torbanite is named after Torbane Hill near
Bathgate in
West Lothian, Scotland, a major location of occurrence.[4] Torbanite found in Bathgate may have formations of
bathvillite found within it.[5] Historically, two other names have been used for torbanite. Boghead coal is named after Boghead estate, also near Bathgate in Scotland. In Australia, the historical name for torbanite was kerosene shale.[6][7]
Organic matter (
telalginite) in torbanite is derived from
lipid-rich microscopic plant remains similar in appearance to the fresh-water colonial
green algaBotryococcus braunii.[1][2][4] This evidence and extracellular
hydrocarbons produced by the alga have led scientists to examine the alga as a source of
Permian torbanites[9] and a possible producer of
biofuels.[10][11] Torbanite consists of subordinate amounts of
vitrinite and
inertinite; however, their occurrence varies depending on deposits.[4]
A rubber-like, elastic, highly-resilient bituminous substance, known as coorongite—classified as an organic-rich sediment and named after the
Coorong where it was found—has been identified as a 'peat stage' in the formation of torbanite. It provides evidence of the lacustrine and algal origin of torbanite.[6][12][13][14][11] Substances very similar to coorongite had other historical names, depending upon the location of the deposits, such as n'hangellite from
Portuguese East African (now
Mozambique) and marahunite from
Brazil.[15]