shale

Meanings

1. 1
   noun

   a fine-grained sedimentary rock formed by compacted clay, mud, or silt, typically laminated and able to split into thin layers

   The road cut exposed thin beds of dark shale between layers of sandstone.

2. 2
   noun

   oil or gas production from shale formations, or the companies involved in that industry

   Investment in United States shale increased after energy prices rose.

Probably from obsolete or dialectal shale ("scale, shell"), from Middle English and Old English scealu ("shell, husk"). The geological sense arose from the rock's laminated structure and tendency to split into thin, shell-like flakes.

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