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Gemstones, Minerals & Fossils
Gemstones and Minerals
Chalcedonized petrifed wood from volcanic area
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<blockquote data-quote="user 4386" data-source="post: 288537" data-attributes="member: 4386"><p><strong>In summary, I tend to think that the reason I assumed petrified wood to be usually of volcanic origin is because is that is likely to be the case for thousands of kms around where I live. Accordingly, I think volcanically-derived silicified wood likely makes up a not-insignificant portion of all the material in Australia, perhaps even a fifth or a quarter.</strong></p><p></p><p><strong>Does anyone have any thoughts on the matter?</strong></p><p></p><p>I mentioned in an earlier post that precious opal in volcanic rocks was minor and rare in Australia, and I quoted some of the few localities where it has been recorded, mentioning one in New England (meaning the broader New England fold belt), Beechworth, Coolgardie etc. I've looked it up, and the New England area is the area around Springsure. So I won't argue the point - you seem to be looking in an area noted as one of the few areas in Australia where silica forming gems related to volcanics is known to be important. So we are talking at cross-purposes a bit..... </p><p></p><p>However I still doubt the fossil wood is related to volcanism (the precious opal in volcanic vesicles at Springsure may be). I mentioned 3 methods of formation and that direct relationship to silica related to volcanic activity was quite rare that a fairly common method of formation, that resulted in a SPATIAL relationship to volcanics, is that as the volcanics (which can be tuff) decompose, their silica is released into groundwater which then travels through gravels etc and replaces any wood present (long after the actual volcanic activity). This describes the process.</p><p></p><p><a href="http://geology.com/stories/13/petrified-wood/" target="_blank">http://geology.com/stories/13/petrified-wood/</a></p><p></p><p>Petrified wood is common in Victoria and much appears to be more than 100 My older than any volcanics (eg in the Otway Ranges).</p></blockquote><p></p>
[QUOTE="user 4386, post: 288537, member: 4386"] [b]In summary, I tend to think that the reason I assumed petrified wood to be usually of volcanic origin is because is that is likely to be the case for thousands of kms around where I live. Accordingly, I think volcanically-derived silicified wood likely makes up a not-insignificant portion of all the material in Australia, perhaps even a fifth or a quarter.[/b] [b]Does anyone have any thoughts on the matter?[/b] I mentioned in an earlier post that precious opal in volcanic rocks was minor and rare in Australia, and I quoted some of the few localities where it has been recorded, mentioning one in New England (meaning the broader New England fold belt), Beechworth, Coolgardie etc. I've looked it up, and the New England area is the area around Springsure. So I won't argue the point - you seem to be looking in an area noted as one of the few areas in Australia where silica forming gems related to volcanics is known to be important. So we are talking at cross-purposes a bit..... However I still doubt the fossil wood is related to volcanism (the precious opal in volcanic vesicles at Springsure may be). I mentioned 3 methods of formation and that direct relationship to silica related to volcanic activity was quite rare that a fairly common method of formation, that resulted in a SPATIAL relationship to volcanics, is that as the volcanics (which can be tuff) decompose, their silica is released into groundwater which then travels through gravels etc and replaces any wood present (long after the actual volcanic activity). This describes the process. [url]http://geology.com/stories/13/petrified-wood/[/url] Petrified wood is common in Victoria and much appears to be more than 100 My older than any volcanics (eg in the Otway Ranges). [/QUOTE]
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Gemstones, Minerals & Fossils
Gemstones and Minerals
Chalcedonized petrifed wood from volcanic area
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