Igneous Rocksgreenspun.com : LUSENET : Introductory Geology, Oswego State : One Thread
In class we talked about how Vesicular rocks are formed from gas bubbles in magma and how when magma cools it shrinks, so does that mean that the holes in the rock were shrunk into different sizes as it cooled?
-- Alison Spring (firstname.lastname@example.org), October 29, 2002
The shrinkage I was talking about actually goes on even when the rock is completely solid. At that point, the vesicles have all formed -- their sizes and shapes depend on the gas bubbles that were forming when the lava was still molten. After the rock is solidified, further cooling causes cracks (geologists call them "joints") to form. These joints are often hexagonal (6-sided, forming a honey-comb-like network) in cross-section. The sizes of the vesicles probably does not change due to shrinkage.
-- Sharon Gabel (email@example.com), November 03, 2002.
I think the hole will not get smaller but it will get closer together, so it will be easier to weather. But I dont think the holes get smaller though
-- Anthea Jeffrey (firstname.lastname@example.org), October 29, 2002.