Meaning & use
combustible rock
A rock that can catch fire and burn, most commonly coal, formed from compressed ancient plant matter.
See it in a sentence
Coal is the best-known combustible rock, mined for use as fuel worldwide.
Geologists classify oil shale as a combustible rock because it contains enough organic material to burn.
A note on using this word
The phrase most often refers to coal, though shale and other rocks rich in organic material can also be combustible.
Words with a similar meaning
fuel rock
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