Looking at the images, and comparing it to other known samples of chalcedony, I am inclined to believe that it falls into 1 of 3 possibilities:
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(and possibily the least likely) There may have been a localized mass of chromium present when this sample formed. The greenish-grey portion is reminiscent of Aventurine, which is chalcedony which often times contains Chrome-bearing fuchsite. I would like to know if any optical phenomena might be present if that section was cabbed and polished. Aventurine also forms in brownish colors as well, and the images seem to show a highly reflective shimmer within the brown sections.
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A variant of 1. Chalcedony is capable of forming psuedomorphs, ie: replacing one mineral with another, in this case, the chalcedony replaced what was originally around the core material green/copper material. The core material might not even have to be “native” to the geologic processes that formed the chalcedony. Chalcedony has been known to replace various shells and other forms in the pseudomorph process, much the same way opal, hematite, and pyrite has been known to do.
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the core material simply served as a seed point that the chalcedony was able to latch onto to begin its growing process. Chemical reactions between the seed and the solution that the chalcedony was suspended in may have resulted in the color-shift in the seed.
Chalcedony has a good degree of solubility in water, so its strongly possible that the sample you have was formed via hydrous deposition. at 100C, you can have up-to 40mg per liter of the microcrystaline silica dissolved in water, and as the water evaporates out, the chalcedony would gradually build up, surrounding whatever is present at the time of formation. This mechanism is how chalcedony is able to form pseudomorphs & may also potentially use a non-chalcedony nucleus for a seed.