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Gold Prospecting
Metal Detecting for Gold
Has anyone come accross rocks like this?
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<blockquote data-quote="Keen Ken" data-source="post: 359966" data-attributes="member: 211"><p>Firstly, I'm not a geologist.</p><p>I think you will find they are the same thing that we refer to in the boulder opal industry as "Ironstone concretions" .</p><p>Thought to have formed when iron accumulates through solution in sandstone. Classed as sedimentary, some of the ironstone and manganese forms i've seen (botryoidal shapes) can resemble something that has formed volcanically or has a "fused " look to it, like your picture .</p><p>This is what the "Yowah nuts" are.</p><p>I have found such concretions from my back yard near Brisbane to all the furtherest Queensland boulder opal fields.</p><p>Boulder opal is formed in them when rare geological sequence line up. the opal can be deposited during or after the formation of these "Boulders" (Larger ones) or "Nuts" smaller ones.</p><p>They usually can be found where there is plenty of iron banding in sandstone formations. Around Wivenhoe Dam where sandstone is eroded is one place I have found them, mostly with a small gravelly coating.</p></blockquote><p></p>
[QUOTE="Keen Ken, post: 359966, member: 211"] Firstly, I'm not a geologist. I think you will find they are the same thing that we refer to in the boulder opal industry as "Ironstone concretions" . Thought to have formed when iron accumulates through solution in sandstone. Classed as sedimentary, some of the ironstone and manganese forms i've seen (botryoidal shapes) can resemble something that has formed volcanically or has a "fused " look to it, like your picture . This is what the "Yowah nuts" are. I have found such concretions from my back yard near Brisbane to all the furtherest Queensland boulder opal fields. Boulder opal is formed in them when rare geological sequence line up. the opal can be deposited during or after the formation of these "Boulders" (Larger ones) or "Nuts" smaller ones. They usually can be found where there is plenty of iron banding in sandstone formations. Around Wivenhoe Dam where sandstone is eroded is one place I have found them, mostly with a small gravelly coating. [/QUOTE]
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Gold Prospecting
Metal Detecting for Gold
Has anyone come accross rocks like this?
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