Deleted
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Post by Deleted on Jun 12, 2013 12:34:56 GMT -5
In lapidary class the terms Travertine and Onyx are interchangeable and at the whim or custom of the person saying it.
In the first few months here at work I got the impression the difference was in the cut. Onyx cut to show the layers and travertine cut parallel to the layers.
Now I am seeing that onyx is rarely used in homes and it is nearly all travertine. Inquiry into the sales representatives seems to indicate that onyx and travertine are the same thing made two different ways.
Their explanation is this: Onyx is layered and usually not so vuggy due to it's aquatic origins. Layer upon layer set down over time as a great body of water dried up.
Travertine is vuggy and full of holes due to it's geyser origin. Thus a cheaper stone due to it's less stable form.
My guess is what the building industry calls travertine would rarely if ever be used in a lapidary sense. But we use onyx all the time.
Does anybody have input that might help set me straight? I am so cornfused.
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Post by orrum on Jun 12, 2013 13:06:19 GMT -5
What about Phils beautiful travertine cabs?
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Don
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Post by Don on Jun 12, 2013 13:17:18 GMT -5
Travertine and calcite onyx are the same thing IMO. True onyx is a variety of banded agate.
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Post by deb193redux on Jun 12, 2013 13:36:23 GMT -5
Don has got it right. Some things called onyx contain calcite, e.g., honey onyx (e.g., www.etsy.com/listing/101144432/honey-onyx-hand-cut-designer-freeform). It is softer, but not as soft as most travertine onyx. Some small amount/parts of travertine onyx are harder and take better polish - even within a few inches in the same boulder. Historically, agate was only fortification or curved bands. They could not assay micro-crystalline structure or do x-ray diffraction to get mineral composition. Other SiO2 with parallel bands was called onyx. (You also had distinctions of black onyx vs red onyx, i.e., sardonyx). Not so much to do with angle of cut, but in small nodules, the bands tend to curve and follow nodule wall. In very large nodules or seam agate, any bands/line may not show any curve over smaller areas. Translucent agate with no bands a all was often call chalcedony. So you have some historical banding taxonomies intersecting some misnamed mineralogy (e.g., calling calcite minerals onyx)
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Post by Deleted on Jun 12, 2013 14:10:40 GMT -5
What about Phils beautiful travertine cabs? I dunno, what about them? Phil, feel free to chime in. My goal is knowledge!
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Post by Deleted on Jun 12, 2013 14:17:41 GMT -5
Daniel you have added another term - travertine onyx! ouch!
I am aware of the historic usage of the term onyx for agates. That seems to have originated in Germany and then for dyed materials. Like I said, I am not expert, so I could easily be wrong.
Don, for lapidary purposes you consider travertine/onyx the same thing. Thank you.
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Don
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Post by Don on Jun 12, 2013 14:44:55 GMT -5
I avoid calling calcite and limestone (travertine) based lapidary materials "onyx" as much as possible due to the confusion with the agate material. For lapidary purposes, I consider both the calcite and travertine stuff to be the same thing since they cut similarly.
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Post by Deleted on Jun 18, 2013 13:56:32 GMT -5
Thanks Don. Your input is gratifying. I think the home improvement industry usurped "travertine" so they could utilize low quality stones with many voids. This is what the builders call "travertine" Something we'd call leaverite they sell for $20-$30/lb!!
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Post by johnjsgems on Jun 18, 2013 18:36:39 GMT -5
That pictured stone is just limestone to me. In the old days when rocks were still cooling, onyx was agate with repeating patterns. Travertine was limestone formed in layers. Some travertine is called "onyx" but in quotes since it isn't really onyx but travertine that looks like onyx. Same with various calcites if they show any "onyx" patterns.
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Post by Deleted on Jun 19, 2013 13:03:53 GMT -5
Thanks John. The building industry identifies limestone formed by geysers, such as what I posted above, as "travertine".
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Post by johnjsgems on Jun 19, 2013 16:32:53 GMT -5
Maybe their names are as accurate as the rock people.
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Post by helens on Jun 19, 2013 22:20:28 GMT -5
I just saw the most astonishing countertop material ever, it was honey onyx, and 11+ feet long and over 5' wide with the most flawless pattern with no fractures... 1 1/4" thick. I'm never going to look at onyx jewelry the same again after seeing a piece that big O.O.
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Post by johnjsgems on Jun 20, 2013 10:50:12 GMT -5
Helen, next time you see some nice black onyx jewelry just picture the Chinese cooking and coloring it.
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