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Author Topic: Rock of the Week (Southwest Oregon, near Agness, OR, Coastal Range)?  (Read 6804 times)

Offline CliffordK

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This rock was found in Southwest Oregon, from a few miles south of Agness, OR, Coastal Range.

It is naturally shiny.  Unpolished.
Magnets will weakly stick to it.





Slight greenish tinge to it in several places.

Weighs about 20 lbs.


 

Offline imatfaal

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Could it be Awaruite?  Looks like a rounded (by river tumbling?) and duller version of this and it is in the right area.
 

Offline Bass

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Given the glassy look, abundance, location and slight magnetism, my first guess would be some sort of basalt.
Basalts are iron-rich volcanic rocks, which explains both the magnetism and glassy texture.  The green is probably either zeolite or some other alteration product.
 

Offline CliffordK

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Could it be Awaruite?  Looks like a rounded (by river tumbling?) and duller version of this and it is in the right area.

I think you are onto something.

At least very close.

Btw, Nickel Mountain is about 50 miles to the north.  But, that was a lot lighter in color.  But, nickel wouldn't be unexpected.
http://www.mindat.org/loc-150587.html

Yes it was a river rock.

And... there was a history of Giants in the area.

But, it certainly is much more polished than the granite that is also nearby, along with a variety of other rock types.

I think I had found some smaller greenish fragments that also seemed smooth and polished, with fresher cracks, but I'm not sure where they're at at the moment.

However, Awaruite appears to be "Strongly Magnetic" by the descriptions.  As I said earlier, this was weakly magnetic (magnets would weakly stick to it)
Also, that seems to be a lot redder than what I have.  This one has greens and blacks, but very little red.  

See notes on Awaruite:
http://www.mindat.org/photo-146564.html

Anyway...  Bouncing around, some things seem to be pointing to a mysterious rock appropriately named "Oregonite", which appears to be related to Westerveldite
http://www.mindat.org/min-4273.html



I also bumped into Serpentinite
http://www1.newark.ohio-state.edu/Professional/OSU/Faculty/jstjohn/Common%20rocks/Serpentinite.htm


So the question is whether this has Arsenic or Silicates in it, or both.

Does everyone just make up a new name when they find a "new" rock?

Yes, there are various igneous rocks in the area.  Both a very dark green with light green veins.
 

Offline imatfaal

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I wish I was - but if Bass says basalt, I would probably put my money on him rather than me (what a sad state of affairs. 

OTOH - I do hope it turns out to be CliffordK-rite
 

Offline Bass

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Westerveldite (and Oregonite) are metallic minerals.  Is your specimen metallic (maybe the photo doesn't do it justice)?

Serpentine is a metamorphic/alteration product of mafic igneous/volcanic rocks (like basalt).  They are most commonly found in areas where seafloor material has been added to continental margins (island arc accretion).  Southwest Oregon has loads of serpentinite.  Nickel-Cobalt-Chrome deposits have an affinity for mafic rocks, which is why you find them in SW Oregon.
 

Offline CliffordK

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Thanks.

As mentioned, a strong magnet (NdFeB) will weakly stick to it in several places, but not uniformly.  So, it would be ore laden. 

However, it is not metallic per se.  I.E.  I have not doubt that it would fracture when hit with a hammer.  While there may be some weak browns/tans, it doesn't seem to be iron oxide colored.

I also checked it with my multi-meter, and it is non-conductive to the resolution of my multi-meter.

So, I would have to conclude that it is non-metallic.

The glassy sheen seems to be intrinsic to the rock.  As mentioned above, it was a "river-rock", but few river rocks get that kind of a sheen.

Black & White granite is common in the area, although some of the granites vary in color including green & white, which would be consistent with the Metamorphic Rock. 

The Cascade Range is generally Volcanic.  This is a little more to the west of the main Cascades, but it cold be related.  However, I don't think it would fall in the Volcanic Glass category.

So...
Lets go with the Serpentine/Serpentinite.

Thanks
 

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