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Post by akansan on May 13, 2008 13:02:01 GMT -5
Okay. I just recently purchased a book on metal smithing (Complete Metalsmith by Tim McCreight) that had a section on stones - the 40 most popular stones in smithing or something like that. One of the things they noted was whether a stone was opaque or translucent. All well and good, right?
My simple mind wrapped itself around the problematic topic this way a long time ago:
Agate = Chalcedony
Jasper = Chalcedony
Jasp-Agate = Chalcedony
Quartz = quartz
Chalcedony = quartz
Flint = quartz
Chert = quartz
Quartz = transparent
Jasper = opaque chalcedony
Agate = transparent/translucent chalcedony
All agate in my mind was transparent or translucent. All jasper in my mind was opaque. Quartz as a subcategory of quartz (amethyst, citrine, etc.) was basically transparent. If quartz (as a main category) was opaque, the item was either flint, chert, or jasper. If it was transparent to translucent, it was either quartz or agate (or quartzite).
I realize this is very simplified, but that was how I possibly incorrectly wrapped my head around it all.
Now to bring it back to the book. According to this book, which is one of the most recommended books for beginning 'smiths, Agate is OPAQUE. In fact, the only transparent/translucent stone they listed in the the quartz family were semi-precious gems such as amethyst.
Eh? It didn't even go into the whole "agate must be banded" debate. It just said it was opaque. Help?
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rallyrocks
fully equipped rock polisher
Member since November 2005
Posts: 1,507
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Post by rallyrocks on May 13, 2008 15:27:21 GMT -5
In general I would not trust a book on metalsmithing to be an expert reference on stones, at the same time I wouldn't look for a book on stones to have expert information on metallurgy
So in this case, I think your "rules of thumb" for quartz family classifications are more correct than Tim is.
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Post by akansan on May 13, 2008 15:30:12 GMT -5
That was my feeling as well. It highlights some of the problems in the jewelry field, though, with the misnaming of stones. I guess I figured someone would have proof-checked his information before allowing it to go to print in such quantities, ya know?
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Post by deb193redux on May 13, 2008 22:51:04 GMT -5
The book is just wrong. Although, my understanding is that it is macro vs micro-crystalline structure that distingushes quartz fram agate and jasper. ALso, the microcrystalline structure of agate and jasper did differ slightly producing the different translucency/opaque - with some exception. FLint/chert is also mictocrystalline, and sometimes the fiact that it ocurs as nodules in sedementary fomrations, with the silica transported form marine fossile sources (as poopsed to vulcanic) i ssometimes made. BUt flint ridge flint is clearly bedrock and not a nodlue so there are always exceptions.
My system is a lot simplier. DO Ilike it? Can I cut it? WIll it polish?
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Post by akansan on May 13, 2008 23:19:07 GMT -5
Dan, I'm right there with you. And I agree on the macro versus micro crystalline structure. I was just talking about how I tell if the stone I'm looking at is agate or jasper, LOL!
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Post by johnjsgems on May 14, 2008 1:19:14 GMT -5
My two cents. Agates are translucent generally when sliced thin and jaspers are opaque no matter how thin you slice them. There are always exceptions (Montana agates for one). Maybe the metalsmith was trying to simplify the difference between agates and quartz family crystals
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Post by larrywyland3 on May 14, 2008 6:24:46 GMT -5
I agree the book got it wrong. Jewelers are usually focused on the metal end and buy stones. Transparent and translucent are words with meaning beyond the lapidary. The books reference of Transparent may be a reference to clarity. Most lapidary materials we cab are not facet quality; meaning they won't refract light and sparkle when faceted. So I am guessing they are trying to distinguish between facet and cabbing materials. IMHO
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Post by bobby1 on May 15, 2008 13:29:59 GMT -5
Here's a diagram that I have used to help clarify the various forms of quartz.  Bob |
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rockdewd
has rocks in the head
Member since October 2007
Posts: 605
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Post by rockdewd on May 15, 2008 15:24:00 GMT -5
As a metalsmith I have only respect and admiration for Tim McCreight. But at a rockhound (lapidary) I can say he is wrong in his simplistic classification. Since I go both ways (get your mind out of the gutter. I'm talking metalsmith and rockhound) I can use my rock knowledge to inform my customers of the type and origin of a particular stone. It is really a good selling point if you can tell customers how the Maw Sit Sit was smuggled out of Burma or how the Lapis was smuggled out of afganistan through the mountains on the back of burros. It adds a little intrigue to the piece. Most metalsmiths know there stones as the pretty purple one.
Bob, thanks for the diagram. I saved it off for future reference.
Rick
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cutter
starting to spend too much on rocks
Member since February 2008
Posts: 129
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Post by cutter on May 15, 2008 15:51:11 GMT -5
Love the petrified tree.
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Post by cpdad on May 24, 2008 21:59:05 GMT -5
i like the tree....but my agate and chert are on 2 different limbs....and yet they seem to be intertwined.....i thunk i need squirrels to jump through the trees and tell me something ;D.
all kidding aside....why do i find agate embedded in my chert....it has been discussed before with no explaination....maybe that there tree can help...maybe...kev.
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Post by johnjsgems on May 25, 2008 8:33:15 GMT -5
I always heard chert was agate without banding/markings. In Ca it is found in the same areas. If you want solid colored agate it is referred to as black agate or the rootbeer colored stuff common on some of our beaches.
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Trilobite
noticing nice landscape pebbles
Member since March 2007
Posts: 77
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Post by Trilobite on Jun 4, 2008 14:17:21 GMT -5
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Post by parfive on Jun 4, 2008 15:00:47 GMT -5
Trilobite - Good read . . . both of them. Thanks
Aggies Rule!!!
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