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Pyroclastic rocks are formed from lavas which are ejected into the air, as occur in pyroclastic flows or Plinian eruptions. They include pumice, volcanic bombs, ignimbrite and ash. The airborne fragments themselves are called pyroclasts (often abbreviated to clasts) or tephra. If they conglomerate into solid rock when they land and cool, then they become a pyroclastic rock called tuff. If they do not then they are still called tephra.
The word is derived from Greek pyro, meaning fire, and klastos, meaning broken; the rocks being "broken by fire".
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