Definitions of volcanic:

• adjective:   explosively unstable

  Example: "A volcanic temper"

• adjective:   relating to or produced by or consisting of volcanoes

  Example: "Volcanic steam"

• adjective:   igneous rock produced by eruption and solidified on or near the earth's surface; rhyolite or andesite or basalt

  Example: "Volcanic rock includes the volcanic glass obsidian"