Wood ?

[fifbrindacier]

My husband found this yesterday, at about 2 400 meters of height, in a place were there is no living trees. The rocks are slates and schists.

It was on an hercynian volcano, rose up from the sea with the formation of the pyrenees mountains 200 million of years ago.

I think it is a piece of wood. It is lighter than the stones of the same size that were around. It also exist a little chance that someone brought it there and forgot it.

[ynot]

Mineralized vein showing "slickenside" characteristics. Not wood.

Tony

[TqB]

I agree with slickenside, from a fault plane.

[DPS Ammonite]

Clean up the end and send a photo. Also take a photo if the other side. It really looks like a metamorphic mica schist and not a piece of wood. When using a magnifying lens, is sparkly mica visible?

Edited August 8, 2016 by DPS Ammonite

[CraigHyatt]

Looks like graphite

[fifbrindacier]

Thanks for your answers, i will put more pics tomorrow.

I hesitated between schist or wood because of the aspect of the other side. But my computer was so long to charge the photos that i couldn't post all of them.

Edited August 8, 2016 by fifbrindacier

[abyssunder]

Not quite visible in the picture, but looks a foliated rock, to me. The foliation could be present in rocks affected by regional metamorphic compression in regions where mountains form. Direct pressure reorients the randomly oriented mineral chrystal grains tending to allign them in a parallel position, perpendicular to the directed pressure. This texture of many parallel minerals makes a schist, which could turn later to gneiss in the metamorphic process (shale>slate>phyllite>schist>gneiss). Schist has a foliated texture similar to wood and can be easily confused with this.

[fifbrindacier]

It reminds me a post i saw that night

Not sure what this is, thanks to anyone who can help

JohnJ identified it as an ironstone or mudstone :

That would explain why there is bryozoans and what look likes a crinoid trace, if i'm not wrong.

There is also a very modern lichen.

[fifbrindacier]

Other pics :

[ynot]

I do not see any fossils in this rock. It looks like a metamorphic rock that has had softer / more soluble minerals dissolved out. I do see some mineralized veins in it.

[fifbrindacier]

[DPS Ammonite]

Other pics :

P8080008.JPGP8080009.JPG

P8080010.JPGP8080011.JPG

Where are these from? Are these side views of the same rock as the first post?

[fifbrindacier]

Clean up the end and send a photo. Also take a photo if the other side. It really looks like a metamorphic mica schist and not a piece of wood. When using a magnifying lens, is sparkly mica visible?

With a magnifying lens and the flash of my camera, it sparkles.

[Ridgehiker]

This type of rock can be difficult to identify without looking at the crystal structure.

At a macro level it looks like a dolomitic limestone that has metamorphosed. Advanced stage of schist. We have lots of this in the Rockies. Usually devoid of fossils but fossils are often found in the adjacent formations above and below.

I've been fooled many times into thinking a rock is petrified wood. When I was a student I once sweated and hauled about a 20 kg rock through the mountains for a day. I proudly brought it to class to show our professor. He looked at it for 5 seconds and just shook his head and said it was a lovely piece of sandstone.

[fifbrindacier]

Where are these from? Are these side views of the same rock as the first post?

Yes they are.

[fifbrindacier]

This type of rock can be difficult to identify without looking at the crystal structure.

At a macro level it looks like a dolomitic limestone that has metamorphosed. Advanced stage of schist. We have lots of this in the Rockies. Usually devoid of fossils but fossils are often found in the adjacent formations above and below.

I've been fooled many times into thinking a rock is petrified wood. When I was a student I once sweated and hauled about a 20 kg rock through the mountains for a day. I proudly brought it to class to show our professor. He looked at it for 5 seconds and just shook his head and said it was a lovely piece of sandstone.

Mine is far less heavy , i didn't know a stone could so much look like wood. I learn everyday in that forum

[DPS Ammonite]

It is a metamorphic rock which is at least partly a mica schist and partly something other where carbonates dissolved.

Does anyone think that you can have mica schist on one part of the rock while preserving convex/concave cavities of dissolved shells on another part? The pressure to form a schist might be strong enough to flatten any shell remnants. Any ideas?

Edited August 9, 2016 by DPS Ammonite

[Ridgehiker]

It is a metamorphic rock which is at least partly a mica schist and partly something other where carbonates dissolved.

Does anyone think that you can have mica schist on one part of the rock while preserving convex/concave cavities of dissolved shells on another part? The pressure to form a schist might be strong enough to flatten any shell remnants. Any ideas?

Good question.

It would depend on what stages the fossils had cycled through previous to its current state. Had brachs, foraminifera shells, etc, silicified? Also something like pyrite preservation in the fossils might lead to cavities.. If the pyrite grains were small to begin with they might not always smear like the big crystals.

The other issue in this is use of terms. Unlike a set definition in a student's geology textbook on the stages of metamorphosed rock, outside the classroom few geologists would be on the same page. There would be too many permutations of minerals to state any absolutes.

[abyssunder]

I think your thoughts are good, Canadawest, DPS Ammonite. I agree with you.

[fifbrindacier]

All this is very interesting. Thanks.

[fifbrindacier]

Marguy told me it could be a piece of Grauwacke with a fault plane slickenside as said Tarquin. I googled it and saw that it is a metamorphic detritic volcano-sedimentary rock of the class of the arenites. That would explain the differences between its slick surface with the other faces and that also would fit with all what you all said.

Even if it is a very common one, i find it awesome to see how much a little stone can tell of the geologic history of its area. This one talks about hundreds millions of years of volcanism, submarine period, tectonic.

I find this very exciting.

Edited August 10, 2016 by fifbrindacier

[Rockwood]

Here's an illustration of a fault with slikensides.

Just because I could

[fifbrindacier]

Here's an illustration of a fault with slikensides.

Just because I could

Your avatar's name is welcome in this post rockwood, thanks for your pic.

Edited August 10, 2016 by fifbrindacier