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Post by Deleted on Nov 24, 2014 22:59:40 GMT -5
Probably. lol But for sure when rhyolites get called jaspers..... However, in another thread Rockoonz said: I have some thoughts about this I wanted to share; so privately I asked Lee to join me in a friendly discussion on this topic. He agreed so now I ask all of you! Lee, would you be so kind as to go into a little bit of detail about the three "jaspers" you mentioned? I ask at the risk of having nothing to say once you are done!
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Sabre52
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Post by Sabre52 on Nov 25, 2014 9:19:05 GMT -5
Very good and tough question. Technically speaking jasper is opaque microcrystalline quartz that is put together as a more or less fibrous mass. Various inclusions cause the colors and patterns and also make it opaque. I think true jasper is igneous in origin. Chert is chemically the same but sedimentary in origin. Silica source for jasper is usually overlaying volcanic ash. perlite etc. examples Bruneau, Willow creek. Source for chert and sedimentary agates is organic ( sponge spicules, radiolarian and diatom skeletons etc). Examples: Morgan Hill and other poppy jaspers which were supposedly , according to some reports, formed as ocean sediments or Mary Ellen Jasper. I'm sure this is an over generalization and that some would take issue with this but that's the way I sort it out.
Most those things we call "picture jasper" are actually a sedimentary stone called pelite, a highly silicified layered mudstone. Not really jasper at all. I suppose you could call them meta-sediments as obviously they are "changed " rocks that have been consolidated and often distorted by pressure and hardened by infusion of silica. I see the Aussie Jasper types (ie Noreena, Munjina, Mook) and Owyhee Jasper as being in this pelite category....Mel
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panamark
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Post by panamark on Nov 25, 2014 13:04:41 GMT -5
Interesting. I always thought jaspers were metamorphic = the intruding silica "changes" the rock. Now the base rock that is being changed can be of many types and that is where the interesting stuff begins.
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Post by Deleted on Nov 25, 2014 15:14:34 GMT -5
Donald Kasper defines jasper as agate with enough iron present to make it opaque.
I want to wait for Lee's reply, because I think my response to him will roll it all up. Maybe. Perhaps.
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Sabre52
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Post by Sabre52 on Nov 25, 2014 16:11:14 GMT -5
OK looked it up: Jasper class is: Silicate----- Subclass is tectosilicate---group is quartz minerals. Jasper. agate etc are cryptocrystalline quartz. According to what I looked up it is a sedimentary deposit that can be found in igneous rocks or metamorphic rocks. I guess that means chert/flint are in sedimentary rocks. The silica is deposited as a sediment in the other rocks, hence the lines, bands, inclusions, colors etc which are the result of deposition of different colored silica containing various colors of mineral salts other sediments etc. ore I look up more complicated it gets....Mel
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Post by Deleted on Nov 25, 2014 16:33:34 GMT -5
yeah, what Mel said. I guess I won't have to wait for Lee to get off from work! Except, why can't it also be a sedimentary deposit in sedimentary rocks? Above you mention Chert and picture jaspers as an example of this. So, I'll go backwards and say agates and jaspers are the same thing, except jasper is an agate that is opaque due to iron content. And those are sedimentary on any base rock/mineral. I say mineral for the concept of gem silica is agatized chrysacolla(sp?) or malachite (hence the two colors). Notice this is also considered an agate as there is no iron present? Plus we have an example of agatized variscite from vegasjames. So, is jasper overused? Not if the stone is actually silicated. But when it's used to name a rhyolite Leopardskin 'Jasper' is a rhyolite, right? Then it's overused. I am sure there are others.
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Sabre52
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Post by Sabre52 on Nov 25, 2014 18:15:05 GMT -5
Scott, maybe I learned it all wrong in geology class or have forgotten what the heck I learned *L* but I was always taught, if its cryptocrystalline quartz in a sedimentary deposit like chalk, limestone etc, it's more correctly flint (in chalk) or chert (in limestone). Oddly enough though, the Hornitos Poppy jasper I collected did not appear to be in sedimentary looking rock but I was told it's actually chert. And the geologic member up there is called Hunters Valley Chert in the books. Dunno about that. Host rock looked pretty igneous or metamorphic to me. Real head scratcher....Mel
And yes, "jasper" is both overused and often incorrectly used.
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Post by Deleted on Nov 25, 2014 19:01:13 GMT -5
well hornitos most definitely has iron in it. enough to be jasper.
Maybe other cherts lack iron and aren't jaspers after all. sheesh!!
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Post by Peruano on Nov 25, 2014 20:11:41 GMT -5
You are all pretty close in realizing that all of them (chert, flint, and yes jasper are all similarly constituted. I just spent several hours on a long train ride and went through my Kindle Geological Dictionary several time wrestling with this one (before the original post). I'll dig out the subtle definitions that I found (after dinner). To be edited later. But all rhyolites are igneous whereas these chalcedony/quartz relatives are capable of being in igneous rocks and metamorphic rocks, they are of sedimentary origin as silicate replacements of other things (including space). Later. Tom
I'm not pretending that this is the end all and be all source of geological knowledge, but thought the definitions in "A concise dictionary of geology" Marie Publications (which I carry on my Kindle) hit the details that sounded reasonable to me.
Jasper is a red, green, yellow, or brown colored type of chert that is opaque and cryptocrystalline in nature.
Chert is a sedimetntary rock that is cryptocrystalline, microcrystalline, or microfibrous and is made up of fine grained silica. Chert is found in a number of different colors that include brown, gray, white, rust red, etc.
Flint, also called flintstone is a type of chert that is hard in nature. It is cryptocrystalline, and sedimentary. It can be found in rocks, lie, limestone, and chalk in the form of nodules.
Chalcedony is a type of silica that is cryptocrystalline in nature and is made up of very fine intergrowths of moganite and quartz. Both of these minerals have different crystal structures. Chalcedony has a waxy luster and can be translucent or transparent.
My (peruano) impression is that the transparent chalcedony is what we typically call agate. And of course agates can take lots of names, based on color. I also suspect that the various colors of jasper reflect different contaminants not just iron. I hope this helps clarify a few grey areas in the definition continuum. Tom
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Post by Deleted on Nov 25, 2014 20:25:49 GMT -5
You are all pretty close in realizing that all of them (chert, flint, and yes jasper are all similarly constituted. I just spent several hours on a long train ride and went through my Kindle Geological Dictionary several time wrestling with this one (before the original post). I'll dig out the subtle definitions that I found (after dinner). To be edited later. But all rhyolites are igneous whereas these chalcedony relatives are capable of being in igneous rocks and metamorphic rocks they are of sedimentary origin as silicate replacements of other things (including space). Later. Tom Yeah, space, like in the mud used to make aussie and owhyee stuff. Nice, tom thanks!
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Post by Rockoonz on Nov 26, 2014 0:57:13 GMT -5
So a replacement is sedimentary, not metamorphic? Even things like petrified wood and limb casts? My knowledge of Geology in the textbook sense could be written on the head of a pin in 26 font. My original comment was more of a musing regarding all the different things out there referred to as "jasper". Perhaps most of the geology I've learned out digging rock with other rockhounds is more like old rock-wives tales. Oregon Sunset "agate" is mostly opaque, does that mean it's really Jasper? Most of the Maury Mt moss agate I have seen is barely translucent at best. See my conundrum?
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Post by Peruano on Nov 26, 2014 7:32:06 GMT -5
Its all really complex and anyone who pretends to know it all is overestimating their understanding. I'm sure geologists would be the first to admit that. Yes we are likely using very loose terminology to describe things we "like". Better a tumble weed in my yard (or cowboy song) than a Russian Thistle. And yes the replacement of some minerals with silicates is likely to be more complex than we are able to grasp in the sedimentary process and then remodeled in the metamorphic processes that can occur subsequently. All points made previously by others are accepted. Take home message offered here is: Not all things that look like something are that something. The proof is in the chemical and crystallography and ultrastructural analysis which we rarely do or have available for the material we have in hand. Have a safe and happy holiday with friends, family, and neighbors. I'm going out to look for rocks on Friday -- they are the best bargains. Tom
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