Fragments of volcanic rock and ash that build up to form cinder cones are known as what?

Cinder cones are known as Scoria cones. These are cones made of basalt at low density. Gas bubble, making up the lave are energetic in nature, because they keep on expanding in all directions, they will go all out to the only open are of a volcano, the vent, in an upward direction. These fragments are called pyroclasts. When thrown up high, because pf pressure, these fragments fail to stick together and cool down before they reach the land making scoria cones.  

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