Answer:

pluton

AnswerCrossword Clue
PLUTONIgneous rock far beneath the earth's surface
PLUTONRock mass within the earth (P.L.O. NUT anag.)
PLUTONIgneous rock that solidifies deep in the earth
PLUTONMass of crystallized magma
PLUTONLabel for rejected planets, itself rejected in August 2006
PLUTONIgneous rock beneath the earth's surface