johnd
starting to shine!
Member since May 2015
Posts: 26 
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Post by johnd on May 16, 2017 11:10:39 GMT -5
Is there a difference in the microcrystalline structure of agate formed in fossils (such as the agatized petrified wood of N Arizona) compared to agate in volcanic inclusions (such as Lake Superior agates)?
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on May 16, 2017 15:39:28 GMT -5
Not in any significant way. They are all formed from silica borne in solution (hot or otherwise). Agate/jasper/chalcedony therefore doesn't have a specific structure, even though the microscopic crystals can line up to form fibers and other features (and this can happen within any cavity, often producing multiple features in a single piece). The differences in color and pattern are caused by impurities in the solution, temperature/cooling, multiple instances of the solution being deposited over time and similar factors not having much to do with the nature cavity being filled (except to the extent that other crystallization had already been taking place prior to the silica being deposited and/or other mineral impurities already inside the cavity). Again, this can happen within any cavity being agatized and isn't a difference in structure. If the silica forms spheres in a lattice formation, then you get opal, rather than agate.
Now, if your aim was to attempt to nail down origin, you wouldn't look at structure. Rather, and it would be a monumental task, you would want to look at unique isotopes (or isotope percentages) contained within the sample and compare them against a database containing verified representative samples of chalcedonies collected from around the world. Building that database would be the real challenge, and I've not heard that such a thing has yet been attempted.
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Post by adam on May 16, 2017 15:48:41 GMT -5
Not in any significant way. They are all formed from silica borne in solution (hot or otherwise). Agate/jasper/chalcedony therefore doesn't have a specific structure, even though the microscopic crystals can line up to form fibers and other features (and this can happen within any cavity, often producing multiple features in a single piece). The differences in color and pattern are caused by impurities in the solution, temperature/cooling, multiple instances of the solution being deposited over time and similar factors not having much to do with the nature cavity being filled (except to the extent that other crystallization had already been taking place prior to the silica being deposited and/or other mineral impurities already inside the cavity). Again, this can happen within any cavity being agatized and isn't a difference in structure. If the silica forms spheres in a lattice formation, then you get opal, rather than agate. Now, if your aim was to attempt to nail down origin, you wouldn't look at structure. Rather, and it would be a monumental task, you would want to look at unique isotopes (or isotope percentages) contained within the sample and compare them against a database containing verified representative samples of chalcedonies collected from around the world. Building that database would be the real challenge, and I've not heard that such a thing has yet been attempted. One of these days a Rock Tumbling Hobby member is going to build a database for quartz and chalcedony and agate, etc. I sure hope so. People can be meticulous. I, for one, believe it be possible. |
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