What does shale mean?
Shale is a soft, fine-grained sedimentary rock made largely from clay minerals and silt. It forms when fine sediment is deposited in quiet water, usually in thin layers that can later split apart. In geological contexts, shale may contain fossils, preserve evidence of past environments, and serve as a source rock from which natural gas and oil can be generated. The term is especially familiar through the expressions shale gas and shale oil, which refer to hydrocarbons extracted from shale formations. Shale should not be confused with slate: shale is sedimentary, while slate forms when shale or another rock undergoes substantial heat and pressure and becomes metamorphic. Although shale is often described as soft, its properties vary, and some shale formations are relatively hard. The word is consequently both a scientific description of a common rock type and an important term in modern energy discussions.
nounShale is a fine-grained, sedimentary rock composed mainly of clay minerals and silt, typically formed in thin layers. It is often soft or fissile and can split along those layers.
- A fine-grained, sedimentary rock composed mainly of clay minerals and silt, usually occurring in thin layers.
- A fragment or mass of this rock, especially when used as a building or industrial material.
"The workers extracted shale from the exposed hillside, revealing layers that had been buried for millions of years."
"The cliff is composed of alternating layers of shale and limestone."
"The company invested billions in extracting shale oil from the basin."
The plural shales is used for distinct shale formations, varieties, or individual masses of shale; shale is generally a mass noun.
"Different shales can vary greatly in color, composition, and hydrocarbon potential."
The same layered rock that can preserve fossils and ancient environments can also contain the hydrocarbons used to produce shale gas and shale oil.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does shale come from?
The word shale comes through Middle English from Old English sc(e)alu, meaning a shell or scale, and ultimately from a Germanic root associated with splitting or covering. In the modern sense, shale was adopted in the eighteenth century for a finely layered sedimentary rock. Its relationship to words such as scale, shell, and scaly reflects the older sense of a thin covering or layer, as well as a shared Germanic and Indo-European ancestry.
Related word forms
How shale is actually used
Shale is primarily a technical geological term but is widely used in general discussion of energy resources. It is usually treated as a mass noun, although shales can refer to distinct formations or kinds of shale. The adjective shaly describes rock containing or resembling shale.
Easily confused with shale
Shale is a sedimentary rock formed from deposited sediment, whereas slate is a metamorphic rock produced when shale or another rock is altered by heat and pressure.