extrusive (volcanic) rocks

Question 1

what are extrusive (volcanic) rocks

Answer 1

formed from rapid cooling and crystallization of lava and other volcanic material

due to temperature of air or water is much lower than lava

Question 2

how is volcanic glass (obsidian) formed

Answer 2

very fast cooling results in glassy volcanic rock

Question 3

how are vesicles formed

Answer 3

due to gas bubbles in lava or magma formed vesicular, bubbly holes, texture

Question 4

extrusive (volcanic) rocks grain size

Answer 4

rapid cooling results in fine grained crystals (<0.25mm, BGS)

not visible to naked eye, aphanitic

Question 5

what is pumice

Answer 5

if magma is highly charge with gas, frothy mass of bubbles may form resulting in spongy texture, low density