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Author Topic: Agate/jasper  (Read 243 times)

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HOOKEDONROCKS

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Agate/jasper
« on: October 07, 2017, 08:03:17 AM »

nice stuff coming off the saw
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fossilman

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Re: Agate/jasper
« Reply #1 on: October 09, 2017, 07:14:45 AM »

Nice slabs.......What next,cabbing them?
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crashoveroide

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Re: Agate/jasper
« Reply #2 on: November 02, 2017, 02:58:18 AM »

Nice... what is the difference between Jasper and an Agate?
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rocks2dust

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Re: Agate/jasper
« Reply #3 on: November 02, 2017, 09:35:02 AM »

... what is the difference between Jasper and an Agate?

Chalcedony is translucent microcrystalline/cryptocrystalline quartz (i.e., quartz in which the crystals are microscopic and/or submicroscopic in size).

Agate is chalcedony with a microfibrous structure, is translucent and contains banding, moss, sagenite, plume and/or similar features to distinguish it from pieces which lack such internal features (i.e., just plain chalcedony).

Chert is opaque microcrystalline quartz that formed in limestone or dolostone deposits (from silica derived from sea beds replacing other material or undersea vents spewing silca-rich material). Flint is chert that formed in chalk and limestone marl deposits. Radiolarite is a chert that contains radiolaria fossils.

Jasper is formed of tiny, quartz or silica-rich grains welded together by chalcedony and usually occurs in volcanic deposits. Jasper and agate often occur together in the same piece of stone, and when it isn't obvious which is predominant, sometimes gets labeled as "jasp-agate" (though this term has no official standing).

That said, mineralogists and other folks (some of whom want to do away with these terms entirely) have argued over the overlapping boundaries in these definitions for over 100 years, and debates still rage on.

Some materials traditionally called "jasper" are actually cherts or flints, some featureless "agates" would more sensibly be labeled "chalcedony," and that is even before situations that arise after a stone is cut. Example: is it still an "agate" if the lapidary chooses to cut out a portion with no detectable banding from an Ellensburg Blue agate, or must the finished piece thereafter be called "chalcedony" instead of "agate"? Your question might be a quick way to start a fistfight at a bar frequented by mineralogists :laugh:
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