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Gemstones, Minerals & Fossils
Gemstones and Minerals
⭐ Gemstone & Mineral Show n Tell
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<blockquote data-quote="user 4386" data-source="post: 421865" data-attributes="member: 4386"><p>"Obsidian . has a hardness of roughly 5 - 5.5...... On Mohs scale of hardness, obsidian is about 5, which can just be scratched with glass".</p><p></p><p>Most glass is hardness 6-7 (up to 9 for gorilla glass, not used for bottles). Its silica content, which commonly is the main determining factor for its hardness, varies from 50% to 90%.</p><p></p><p>So it is in the eye of the beholder - the problem being that the composition of obsidian varies as much as the composition of glass - it commonly varies from 65 to 80% silica. Your observation might well work using the same piece of glass in a single volcanic province - but you are better than me if you can easily detect 0.5 difference in hardness anyway...</p><p></p><p>I find it bloody difficult in any new area - once I know an area, things like colour are usually more useful, also flow layering and tiny included crystals in obsidian. I doubt that I am ever 100% confident without such features (of course the way it occurs geologically is a clue - if it is not just an isolated fragment)..</p></blockquote><p></p>
[QUOTE="user 4386, post: 421865, member: 4386"] "Obsidian . has a hardness of roughly 5 - 5.5...... On Mohs scale of hardness, obsidian is about 5, which can just be scratched with glass". Most glass is hardness 6-7 (up to 9 for gorilla glass, not used for bottles). Its silica content, which commonly is the main determining factor for its hardness, varies from 50% to 90%. So it is in the eye of the beholder - the problem being that the composition of obsidian varies as much as the composition of glass - it commonly varies from 65 to 80% silica. Your observation might well work using the same piece of glass in a single volcanic province - but you are better than me if you can easily detect 0.5 difference in hardness anyway... I find it bloody difficult in any new area - once I know an area, things like colour are usually more useful, also flow layering and tiny included crystals in obsidian. I doubt that I am ever 100% confident without such features (of course the way it occurs geologically is a clue - if it is not just an isolated fragment).. [/QUOTE]
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Gemstones, Minerals & Fossils
Gemstones and Minerals
⭐ Gemstone & Mineral Show n Tell
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