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Folks on mindat.com suggested asking this question here! This is less of a "what is this a fossil of" question and more of a "is this possible" question. I have a small chip of translucent chalcedony showing a mass of white inclusions, two of which look very much like a grass seed-head. The gist of the conversation so far has been 'is it possible for fossil material to be an inclusion within a silica mineral like agate or chalcedony?' As opposed to an agate-replacement or opal-replacement fossil like an agate limb cast, agatized wood or agatized/jasperized opaque mudstone with intact fossil imprints of leaves and fish. Because pseudo-fossils in chalcedony are so common, with organic-appearing moss, dendrites and "garden" quartz mislabeled as fossil material all the time, there is a knee-jerk reaction of "never." But, am wondering... is it mechanically impossible or just highly uncommon? It has been suggested it may have formed in association with a mineral-rich hot spring, first as opal, then as agate. This was found in the John Day basin, Antelope/Ashwood area of central Oregon, in a drainage downslope from a 15-square mile basin that is ringed with lahar palisade formations (think Clarno palisades from John Day Nat. Monument.) The area has standing agatized tree trunks 5 feet high and 2 feet thick, and is full of smaller petrified wood and plant fossils. Age is 30-40 million years, in an overlap between John Day and Clarno formations. Private property, with permission. Apologies for the quality of the photos, am taking pictures with a phone through a hand lens.
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