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rookie needs help

Posted by matthew spraker  
rookie needs help
March 07, 2012 12:41AM
Ive recently got into rockhounding and am new at this, so heres the best i can do for the description. smooth silky feel with a pinkish tan color with bits of blue black blended in. is the cleavage the 57 degrees, im pretty sure its not 90. the side not cleaved in which i included in the pics seems more grayish tan and has a finely grained texture. im guessing that the weather has an effect on the exposed side causing the different texture as compared to the cleaved sides. am i right and does this happen to alot of rocks. seems kinda heavy for its size. found in southwest virginia. thank you for your time. i do have the national audubon field guide but seems a bit overwhelming to me. thank you for your time.
open | download - DSCF2660.JPG (106.4 KB)
open | download - DSCF2661.JPG (118.5 KB)
open | download - DSCF2662.JPG (128.4 KB)
Re: rookie needs help
March 07, 2012 01:08AM
Hello Matthew and welcome to mindat!!!

A bit more information would help. First, your photos are great but we need some diagnostic data: can you make a scratch in the specimen (that will catch your fingernail) with a knife blade? Will it scratch glass? Does it leave a colored streak on unglazed porcelain (the underside of your toilet tank cover)?

A first guess would be chert. I don't see a cleavage, just some cracks and spalling and a hint of a conchoidal (shell-like) fracture.

Get back to us with some more data.....

avatar Re: rookie needs help
March 07, 2012 01:40AM
I agree with Don, this material could be many things: feldspar, quartz, limestone...

In addition to what Ron said, to discard limestone you can do a test with hydrochloric acid or vinegar (bubbles).

We wait for your news...

avatar Re: rookie needs help
March 07, 2012 02:03AM
To me, it looks like a piece of quartzite, which is a metamorphosed sandstone.
That would not be unheard of in SW Virginia....
Re: rookie needs help
March 07, 2012 02:19AM
Agreed Paul, I have sold similar pieces labelled as such.

Welcome to mindat Matthew, and goodluck.
Re: rookie needs help
March 07, 2012 03:30AM
scratches glass, scratches my knife, vinegar doesnt have an effect, doesnt seem to leave a definite residue on the two porcelains i tried, maybe slightly grey. thanks for the help everyone!
avatar Re: rookie needs help
March 07, 2012 03:55AM
The perfectly-formed, delicate conchoidal fracture in DSCF2661 suggests chert. The grainy, smoothly rounded surface in DSCF2662 is typical for the exterior of a chert nodule. Coloration is perfect for chert. Chert is also found in SW Virginia. Broken surfaces of quartzite tend to be rough instead of smooth, as in your piece. Chert fractures are rarely rough. I think it's chert.

Good work in finding that and doing the analyses!
Re: rookie needs help
March 07, 2012 05:05AM
I would have to agree it is likely chert. That means the angle you measured is not cleavage, but rather a random angle of breakage on a rock, which is what chert is - an aggregate of microscopic quartz grains.

Good job using the testing methods, and welcome to Mindat.
avatar Re: rookie needs help
March 07, 2012 12:39PM
Jasper? Looks like this one


Edited 1 time(s). Last edit at 03/07/2012 01:31PM by Amanda Hawkins.
avatar Re: rookie needs help
March 08, 2012 12:50AM
Chert, jasper, chalcedony, yes, must be criptocrystalline quartz.

avatar Re: rookie needs help
March 08, 2012 04:07AM
I agree with Norman and Keith's ID of chert.

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