black gold

Noun

black gold (uncountable)

1. (idiomatic, informal) Raw petroleum; crude oil.
   • With the black gold already gushing from his country's wells, the Iranian monarch did not show much interest in what the Republic of China had to offer in agricultural know-how, commerce, and cultural interflow.1983, James C. H. Shen, “Rejoining the Government”, in Robert Myers, editor, The U.S. & Free China: How the U.S. Sold Out Its Ally, Washington, D.C.: Acropolis Books Ltd., →ISBN, →LCCN, →OCLC, page 29
2. Black pepper, in the context of being a historically valuable spice.
3. Black-coloured gold, variously produced by patination, deposition, oxidation, etc. and used in jewellery or in high-technology applications.
4. Coal.
   • They [the railways] are mostly remnants of a long-gone coal industry, laid out largely to bring the black gold from the mines to the waterways.2022 April 20, Christian Wolmar, “Northumberland Line reopening is not the end of the journey”, in RAIL, number 955, page 46