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Need help with oddball rock please.


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1 hour ago, Pumicelady said:

Hi all I found this on the south toutle river in wa.  I think or the area.

Thought was wood but scratches metallic on outside ,non magnetic, streak is blue/gray cuts into plate. Weighs 443.8 grams hardness 5 to 6 smooth greasy feel. Thanks in advance. 

 

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My first impression is basalt. I see flow lines and it does streak gray at times. I'm sure others will chime in.

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I think it is a sandstone with desert varnish on the outside.   The "varnish" has been mechanically worn off producing the "tiger strips" pattern.  Neat find!

Desert varnish = a chemical weathering process that produces a dark "rind" on the outside of a rock, exposed to a desert/semi desert environment. 

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On 9/30/2020 at 9:28 AM, 4meter said:

I think it is a sandstone with desert varnish on the outside.   The "varnish" has been mechanically worn off producing the "tiger strips" pattern.  Neat find!

Desert varnish = a chemical weathering process that produces a dark "rind" on the outside of a rock, exposed to a desert/semi desert environment. 

Definitely not found in the correct environment for desert varnish and being found in an active river would obliterate desert varnish. Could have an oxidation rind but I would not wager on it. Based on the geology of the area it is likely an odd ball metamorphic/igneous rock.

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