Fossil wood or mineral vein?

[Archie]

Heres a further away shot of another sample of rock from the same bed, some of the amygdales have loose double terminated calcite crystals, and the block with the "wood" showing it in the matrix and the contact between the two.

[Archie]

These are both shots of the back of the sample with the wood (color difference is due to different lighting).

[abyssunder]

I would agree that there might be amygdaloids in the last pictures.

[Archie]

My friend is convinced its sandstone and there are occasional tiny rounded grains of quartz but the crystal filled bubbles and just the appearance in general screams to me that its basalt or some other volcanic rock. Its also from a zone sandwiched in between a thick sandstone bed (the Dunnet Sandstone) and a volcanic neck that broke though this bed slightly later in the Lower Carboniferous, the distance between the sandstone outcrop and the exposed volcanic neck is only around 40 yards and this was found on an exposure directly between the two. Unfortunately the contact between any of the the three rock types is not exposed. I'm convinced the matrix is volcanic, and while there is a really nearby site (a mile tops) with permineralised plants preserved in a lava flow they are as stated earlier found in blocks of limestone caught up in the flow, and are are also small fragments preserved in peat. This whole piece is about a foot long and certainly isn't encased in limestone. There were slichensides in the definite basalt exposure just metres away with calcite fibres that looked very similar to this, and were very similar in size, but they were more flattened than these, were only a few mm thick and did not criss-cross at 90 degrees.

[ynot]

The last picture screams pyroclastic flow to Me.

[Archie]

I've been looking up fibrous minerals/crystals and thought this specimen of kyanite had a slightly similar appearance, I just feel that this criss-crossing pattern seems more crystalline than organic and that this would make more sense in volcanic rock. I could be totally wrong though!  

[ynot]

Have You done any tests to determine what minerals are present in the piece?

Hardness, streak and reaction to acid?

 

I can not think of anything mineral that has the features in the close up pictures.

I will go with this being some strange plant structure, maybe an extinct fern family. (just a guess)

[Archie]

10 minutes ago, ynot said:

Have You done any tests to determine what minerals are present in the piece?

Hardness, streak and reaction to acid?

 

I can not think of anything mineral that has the features in the close up pictures.

I will go with this being some strange plant structure, maybe an extinct fern family. (just a guess)

Not yet but next time I'm round at my friends I will do. The close ups of the cross section really do resemble plant, I'm still just puzzled by the structure and how it survived being caught up in molten rock, that is if the vesicles are evidence that this rock was once molten? Do vesicles form in rocks formed by pyroclastic flows? I could see how plant material could be caught up and preserved in a pyroclastic flow.

[ynot]

3 minutes ago, Archie said:

, I'm still just puzzled by the structure and how it survived being caught up in molten rock, that is if the vesicles are evidence that this rock was once molten? Do vesicles form in rocks formed by pyroclastic flows?

All depends on the viscosity and temperature of the "mud" when it trapped the plant material.

Pyroclastic flows are not composed of "molten" rock as such. They are more like a real hot cement or mud mixture.

[DPS Ammonite]

The rock in a pyroclastic flow was not necessarily molten. It however was hot enough for water to boil and form pockets where low temperature minerals such as calcite, chalcedony, quartz and zeolites formed.

 

The plant material may have already been permimeralized when it was caught up in a volcanic eruption/ pyroclastic flow.

 

Kyanite is a metamorphic mineral that would not be found in volcanic rocks.

[DPS Ammonite]

Send some photos of the plant material to Andrew C. Scott who was an author on a paper about the flora near Kingswood. 

 

https://pure.royalholloway.ac.uk/portal/en/persons/andrew-cunningham-scott(be6989a7-c348-48aa-b401-d50d86d451c1).html

 

Studies on a new Lower Carboniferous flora from Kingswood near Pettycur, Scotland. I. Preliminary report

 

 

[Archie]

A chunk of plant that was already permineralized before getting caught up in a flow definitely sounds like the best explanation for this, I'll send some pics off to Andrew C. Scott and report back what he says. Thanks again very much for all your help everyone!  

[Carl]

I'm pretty convinced this is a radial wood section showing the xylem rays crossing the longitudinal wood fibers.