Adjective
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igneous rock produced by eruption and solidified on or near the earth's surface
rhyolite or andesite or basalt
"volcanic rock includes the volcanic glass obsidian"
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explosively unstable
"a volcanic temper"
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relating to or produced by or consisting of volcanoes
"volcanic steam"
"volcanic islands such as Iceland"
"a volcanic cone is a conical mountain or hill built up of material from volcanic eruptions"