Obsidian, DYK Fact #553
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Obsidian, DYK Fact #553| George Law |
Posted: 20:09 Sunday 08 March 2009
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 Nirvana  Group: Moderators Posts: 1 270 Member No.: 3 Joined: 03 Jan 2007  |
I have just read about obsidian in the section on igneous rocks of a little pocket book about rocks & fossils. Did you know? Obsidian is glassy in appearance – indeed, glass is the main constituent of this volcanic rock. The vitreous nature of obsidian means that it can be broken into fragments with very sharp edges – making it ideal for the making of prehistoric cutting tools. -------------------- |
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| Sylvia |
Posted: 18:27 Saturday 28 July 2012
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 Renaissance Group: Friends Posts: 133 Member No.: 170 Joined: 30 Aug 2010 |
Did you know? The vitreous nature of obsidian is due to the extremely rapid cooling of the magma from which it is formed – so rapid that crystals have no time to form and the rock is “frozen” into glass. I have just read the article IGNEOUS ROCKS in Chapter 2, “Earth and its resources”, under the section THE PHYSICAL UNIVERSE in Volume 1, “The world of nature”, of the Reader’s Digest Library of Modern Knowledge.
-------------------- Sylvia A. Anderson
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