Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: ebrintle on 16/02/2014 01:03:41
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I found this hidden behind old wall in a house I am remodeling. It is quite heavy for a 3"x 1"x 2".
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I think I know the rock, It's a quite common river rock. If I am correct and the rock has shiny flaky spots then it's magnitite. But the picture you posted is kinda small I can't be for shore
compare your rock to some of these on this website.
http://quizlet.com/6821355/mineral-samples-adv-gen-geology-flash-cards/
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It is always tricky to attempt this when all one has is a weathered specimen, viewed from a single angle.
The reflecting grains on the top surface could well be mica. There also appears to be some lamination running parallel to that top surface.
The dark colour, coupled with your comments on apparent density suggest a rock rich in ferro-magnesian minerals.
In combination these observations lean me towards saying it is a schist, possibly formed from regional metamorphism of basic lavas, or shallow intrusions. That is, however, quite speculative.
SS - what do you mean by a river rock? I know of no such term, unless you mean a rock to be found as a pebble in a river. In that case it is rather meaningless, since any competent rock can wind up as a pebble in a river.
The density and dark colour do not preclude magnetite, but it seems unlikely. (And lets remember magnetite is a mineral, not a rock.)
Any chance of more photos: different angles, closer, more exposure?
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ebrintle,
does the rock stick to a magnet?
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I uploaded some more photos and can email you some higher def pictures if you like. It does not seem to be magnetic. The house is located in the Blue Ridge Mountains of southern VA. There is a rock in the area but mostly smooth light colored fieldstone and quartz. This black rock is different than anything I have seen in the area. The old farmer who built this 1939 farmhouse must have thought it was valuable.
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Few more pictures.
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Thank you for the further photos. I am now leaning strongly to it simply being a basic lava, probably basalt. The lineations I thought I saw are not schistosity, but may be late stage mineralisation from hydrothermal activity along fine fracture planes. (These are quite clear on Rock.3)
I'm more confident about this than the first one, but still only 70% - 80%.
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ebrintle- how heavy is "quite heavy"? Any chance you could get us a specific gravity? Or how does it compare with ordinary stones about the same size? twice as heavy? three times? more?
Like ophiolite- I can definitely see metallic minerals in photo 3 and 5. Are there any old mines nearby? Hard to tell from just a few photos, but I don't believe the rock is volcanic.