rookie needs help

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.

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.....

Don

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...

Josele

To me, it looks like a piece of quartzite, which is a metamorphosed sandstone.
That would not be unheard of in SW Virginia....

Agreed Paul, I have sold similar pieces labelled as such.

Welcome to mindat Matthew, and goodluck.

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!

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!

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.

Jasper? Looks like this one

Amanda



Edited 1 time(s). Last edit at 03/07/2012 01:31PM by Amanda Hawkins.

Chert, jasper, chalcedony, yes, must be criptocrystalline quartz.




Josele

I agree with Norman and Keith's ID of chert.