petroglyph
off to a rocking start
Member since April 2007
Posts: 22
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Post by petroglyph on May 9, 2007 4:12:25 GMT -5
I found this 2 weeks ago and now that I've cleaned off all the mud and had a closer look it's got me baffled. When I found it I could see some of the lines in it and I thought "nice piece of petrified wood'. It is not petrfied wood though.... the 'grain' pattern is wrong. It looks like it may be some sort of highly silicified finely banded sedimentary rock, or maybe silicified geothermal sinter. It's slightly translucent and very hard (nicely weather polished in places too) The interesting thing is, at the left side it has been stoved in by some massive impact. It is crushed, distorted, folded and has fractures filled with broken material.... then it has been re-cemented and is very hard and solid..... no crumbly loose material at all. I found this on the shores of the Kaipara harbour here in New Zealand, an area with very complex geology. The distict is known as the 'Kaipara allochthon' which means that the rocks here were formed elsewhere and were transported here over the millenia. Volcanoes have erupted through all this jumbled up rock and added their own flavour just to complicate things too. Has anyone seen this type of rock before (never mind the stoved in area)? Cheers, Tim.
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181lizard
Cave Dweller
Still lurking :)
Member since December 2005
Posts: 2,171
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Post by 181lizard on May 13, 2007 12:59:05 GMT -5
Hi Tim...well, I know squat about alot of things, but this formation has shown up in rock/land masses in many different books and articles. If I can run across one, I'll pass you the info. It's like...as the liquid moves, it's bent or something impedes it's forward movement so it goes around obsticles or as it's moving, another motion or action causes it to change direction & bend. (someone out there will correct my poor attempt to explain...please?)
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Post by freeform on May 13, 2007 21:49:01 GMT -5
Ive seen allot of Nevada Wood resemble that similar looking formation. The opal wood from the Vrigin Valley is often contorted, smashed, broken and recememnted back together. Looking at your photos i would say wood, but having no experince with rocks from that neck of the world, i have no clue. The metamorphic rocks of Arizona ive seen produce similar layered patterns, were you can see the folding and bending of the rock at one time in its life. But these are not agate like that piece you got there. Any idea of Petrified wood from New Zealand? If so, thats were i would start, ebcasue there is bound to be someone of some group that collects it. Then at least you can get a diffinitive NO for the those that would really know best. Neat looking piece for sure.
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desertdweller
fully equipped rock polisher
Member since August 2006
Posts: 1,803
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Post by desertdweller on May 14, 2007 8:56:02 GMT -5
It looks like serpentine to me. Did you do a hardness test on it? Serpentine is a lot softer than pet woods, I would suggest a hardness test but I am pretty sure its serpentine.
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Post by goldfinger on May 14, 2007 12:18:21 GMT -5
Looks like some kind of schist to me... Seen plenty the same type of rock in Nevada.
Steve
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Post by Deleted on May 18, 2007 1:29:35 GMT -5
I just had a science lesson at school on rocks and held a schiest in my hand and I agree with Steve, it looks a lot like a schiest.
Nathaniel
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fossilman
spending too much on rocks
Member since April 2007
Posts: 256
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Post by fossilman on May 18, 2007 18:00:22 GMT -5
it's not a schist, they tend to be extremely micaceous, and I see no mica in it. I would guess serpentine. How strong is the rock? If you can peel off strings of it, or chip off strings, it may be chrysotile (asbestos)
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petroglyph
off to a rocking start
Member since April 2007
Posts: 22
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Post by petroglyph on May 20, 2007 4:10:47 GMT -5
Hi folks, thanks for the replies. Firstly I am very familiar with petrified wood from the whole region and I can definately rule it out as a possibility. At first glance it looks like a wood grain but on close inspection it is simply alternating layers that sometimes coalesce into each other.... wood doesn't do that; each yearly growth ring is separate from the others. There's no cellular pattern either. It's not schist either.... as Fossilman says, schist usually has specks of mica all through it. It's usually softer as well. Nor is it serpentine... this stuff is very hard and is silica (quartz) based. I just did a test on it... it doesnt scratch a good solid piece of Brazilian agate and the agate doesn't scratch my rock either. Makes me wonder if it might be a pseudomorph of serpentine... if there is such a thing.
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Deleted
Deleted Member
Member since January 1970
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Post by Deleted on May 22, 2007 6:40:38 GMT -5
what is the yellow on the rock? Does anyone know?
Nathaniel
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petroglyph
off to a rocking start
Member since April 2007
Posts: 22
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Post by petroglyph on Jun 2, 2007 0:14:27 GMT -5
I think the yellow is just where some of the layers have partially separated and they are slightly translucent
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rockinmom
spending too much on rocks
Member since January 2007
Posts: 481
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Post by rockinmom on Jun 9, 2007 18:24:09 GMT -5
Has anyone figured it out yet? T.
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