earthstory: Copper replacement The beautiful translucent grey fortification agates (so called becaus
earthstory:Copper replacementThe beautiful translucent grey fortification agates (so called because the lines resemble the crenulations of castles or the rings of fort walls seen from above) found in parts of Michigan are unique in their fiery beauty, induced by traces of native copper (visible as the reddish metallic flecks and lines) that infiltrated in a molten form as the agates were precipitated replacing some of the rings. Some 1.1 billion years ago the nodules of microcrystalline silica precipitated from fluids and gels into the gas bubbles in basaltic lavas. Keep reading -- source link
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