extrusive (volcanic) rocks Flashcards
1
Q
what are extrusive (volcanic) rocks
A
formed from rapid cooling and crystallization of lava and other volcanic material
due to temperature of air or water is much lower than lava
2
Q
how is volcanic glass (obsidian) formed
A
very fast cooling results in glassy volcanic rock
3
Q
how are vesicles formed
A
due to gas bubbles in lava or magma formed vesicular, bubbly holes, texture
4
Q
extrusive (volcanic) rocks grain size
A
rapid cooling results in fine grained crystals (<0.25mm, BGS)
not visible to naked eye, aphanitic
5
Q
what is pumice
A
if magma is highly charge with gas, frothy mass of bubbles may form resulting in spongy texture, low density
