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#11
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choosing tools for working jasper/chalcedony/quartz
On Jun 25, 12:46=A0pm, Peter W. Rowe
wrote: On Tue, 23 Jun 2009 10:00:20 -0700, in rec.crafts.jewelry sunrainor wrote: And not sure how to do this, but I'd like to be able to tell people what my stones actually are - from what I read, it's quite difficult to actually pin down unless you are either an expert of can do some tests...where does one look for help in this? If your stones are, indeed (as the thread title suggests) Jaspers, chalce= donies, or other quarts based materials, then you may indeed have a hard time pin= ning things down to an exact name. =A0The reason is simple. =A0There may not a= ctually be an exact name for a specific variety. =A0 All these materials are essenti= ally minor variations on the same stuff. =A0 Quartz is a very common mineral. = =A0When you get single solid crystals of the stuff, it can be various colors dependin= g on what impurities are in it, thus we get purple quartz called amethyst, orange/yellows called citrine, etc. =A0 That's the simple part. =A0After = that, it gets a bit trickier. =A0Quartz also commonly forms not as single large cr= ystals, but as a mass of many microscopic crystals, often mixed in with other min= or componants which can change the appearance or give it color. =A0When not = much else is in it, the color is a milky white, rather transluscent. =A0If that's a= mass without structure, we just call it chalcedony, which is sort of a generic= catch all catagory rather than a specific type, since that also includes a numb= er of varieties that have various colors too. =A0When that chalcedony forms as = banded layers, laid down from a water deposit, then we call it agate. =A0Same ma= terial, but the name refers to the banded structure. =A0Agates too, come in a wid= e range of appearances, some of which get named for that specific appearance or m= ore often, the most well known source. =A0Some agates, like moss agate, may n= ot have such a strong banded structure, but they still get called agates. =A0 Whe= n the impurities get to a large enough layer that the pigmentation they give me= ans the rock is no longer transluscent, but rather an opaque colored mass, then i= t often gets called jasper. =A0Again, it's the same basic type of material, diffe= ring in the amount or color of the impurities. And then the jaspers get named oft= en for where they are found, or for prominant aspects of their appearance, or bo= th. =A0 The key here, is that agates, chalcedonies, and jaspers are all varieties= of the same mineral forming in slightly different ways with differing appearance= s and structures. =A0So the names given are not organized by a strict mineralog= ical system. =A0If you're in an area which is not well known for it's lapidary materials, then while you may find any sort of nice variety of materials = these may not exactly fit into one or another of the nicely accepted names, so = you may not be able to get more precise than just "jasper" or "chalcedony" or aga= te. And even then, more than a few of these materials are sufficiently mixed with= other minerals that even these names may not be precisely accurate. As you say, an expert in the materials could likely give you a definitive= nice sounding name. =A0But would that name always be exactly right, or differe= nt enough or more accurate from other names one might also have decided on? =A0Not = always. It's a bit of a muddy area, describing a myriad of varieties of different= looks to essentially related materials that all fall within the same set of mineralogical/gemological catagories. There are a few good books published that can give you some clues. =A0Joh= n Sinkankas, quite some years ago, published a fine book on the agates of n= orth america. =A0I'm not sure if that's the exact title, but it's close. =A0Ni= ce illustrations that would help. =A0After that, catalogs showing gems or la= pidary materials for sale will also give you clues as to appropriate names to us= e. Of course, not all lapidary materials are actually quartz based. =A0There= are a large number of other minerals used for gems as well, and each has it's o= wn name or set of names for varieties of that material. =A0Telling these apart so= metimes can be done visually, and sometimes needs specific tests. =A0You can find= a number of good books out there on the subject of gem identification that can giv= e you an idea of how this is done. =A0The classic is Liddicoats "Gem Identifica= tion", the GIA published text on the subject used in their gem identification cl= asses. But there are quite a number of others too. Hope that helps. Peter Rowe Yes indeed it does - I sort of knew this already but you've described it more clearly - I know that St. Lucia in my area (north) has rhyolitic rocks, jasper for sure. It's not well known for lapidary materials at all, but there's definitely a fair amount of these quartz based materials. I'm happy with chalcedony for the translucent off-white-ish ones and jasper for the yellows and reds. There are some that look like jasper mixed in with lava - ie the dark parts have lots of bubbles and are rough - these are much more brittle and I thought I'd call them jasper- lava. Really I just don't want to claim anything that's not true - like I read complaints about people calling non-agates, agate. I believe I will go to the library here and see if there's a rock ID book and if not, I'll go ahead and get one like the one you suggested...I do think someday I'd like to do some rockhounding trip (s) and maybe I'll work with stones that aren't local also. cheers Finola |
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choosing tools for working jasper/chalcedony/quartz
On Jun 25, 12:28=A0pm, Jim wrote:
On Tue, 23 Jun 2009 10:00:20 -0700, sunrainor discovered a keyboard and, for our edification and amusement, submitted As the machine is an all-in-one, you'd probably get the best deal by purchsing the whole kit-and-kboodle. Jim Ahh, that's true - thanks, and for the Google suggestion - will do I finally feel like I'm getting somewhere Finola |
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choosing tools for working jasper/chalcedony/quartz
On Thu, 25 Jun 2009 08:31:45 -0700, in rec.crafts.jewelry sunrainor
wrote: Yes indeed it does - I sort of knew this already but you've described it more clearly - I know that St. Lucia in my area (north) has rhyolitic rocks, jasper for sure. It's not well known for lapidary materials at all, but there's definitely a fair amount of these quartz based materials. Check these definitions. Last I heard, Rhyolite is an igneous rock. Though silica rich, it is not jasper, nor related to it. Jasper, like other chalcedonies, is a sedimentary material. Now, you could have rhyolites with voids, bubbles, etc, form, which later would have jasper or other chalcedonies deposit within those cavities. One classic example of that structure is Mexican opal, which often is found filling holes and bubbles within a rhyolite... But Jasper itself, is not generally referred to as rhyolitic I don't think... I'm happy with chalcedony for the translucent off-white-ish ones and jasper for the yellows and reds. There are some that look like jasper mixed in with lava - ie the dark parts have lots of bubbles and are rough - these are much more brittle and I thought I'd call them jasper- lava. Really I just don't want to claim anything that's not true - like I read complaints about people calling non-agates, agate. Again, I'd wonder just how lava and jasper could mix. This would require a lava deposit below the water table, with sufficient porosity for mineral rich solutions to penetrate the lava and deposit jasper within bubbles or voids. If your material looks like lava has flowed into cracks or seams in the Jasper, then I seriously doubt it's lava. Rather, it's likely something else that could also deposit within cracks or fissures in the Jasper, at low temps, perhaps hydrothermally. Hematite comes to mind... I believe I will go to the library here and see if there's a rock ID book and if not, I'll go ahead and get one like the one you suggested...I do think someday I'd like to do some rockhounding trip (s) and maybe I'll work with stones that aren't local also. Beyond the basic gem identification book I suggested, which concentrates more on classic gems, you may wish to be looking more at mineral guides, and see if you can find some information on the basic geology of your area. If, for example, you're in an area which does not have a volcanic origin, then you can be pretty sure you're not finding lava. But this does not rule out other sorts of igneous rocks (granite, rhyolite, Basalt, etc) It might also be worth trying to see if a local high school or college has anyone teaching geology or mineralogy classes. Those folks might be well familiar with local geology and materials. Peter cheers Finola |
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