expansion of internal gas due to the sharp decrease of pressure after the sudden cooling of magma in the process of volcanic eruption.Its stomatal volume accounts for more than 50% of the rock volume.Because of the pores, light weight, can float on the water and is known as pumice.Its characteristic is high intensity, heat preservation, heat insulation, sound-absorbing, fire prevention, acid and alkali resistance, corrosion resistance, and no pollution, no radioactivity, etc.
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