Petrified wood?

[winnph]

Hi all! Just got back from a weekend hiking along the Olympic Peninsula oceanside beaches with my family. I usually pick up a few beach stones on trips like this, and his particular stone caught my eye because the lighter colored streaks sparkle a bit in an opal-y kind of way. When you hold it to the light you can see a pretty clear wood grain/ring pattern, with the opalized bits filling where you might imagine cracks in the wood to have been. 

I know this is hard to be sure from photos but just curious if others agree that this appears to be petrified wood. 

[Rockwood]

I think it's wood. 

Kind of looks like a crochet ball that got left on the lawn too long.  

[Rockwood]

15 minutes ago, Rockwood said:

Kind of looks like a crochet ball that got left on the lawn too long.

One should always have them over their croquet balls. 

[ynot]

Welcome to TFF!

I think it is a tumbled siltstone, not petrefied wood.

[abyssunder]

What I think is sure for me, is that the specimen has nice percussion marks.

[Zenmaster6]

For this to be petrified wood, it would have to become mineralized with a black mineral and then be tumbled by the ocean or river. Seems unlikely but it could be. I would agree with siltstone hypothesis. Those stripes do look rather "woody"

[winnph]

Thanks, everyone!

 

It's hard to photograph because it's just texture differences on a pretty smooth stone, but here's my best attempt to show the concentric rings in the black stone with the opal-y "cracks" running mostly perpendicular to those rings. When you tilt the stone back and forth, the rings are a lot more wood-y looking than in static photos because they look like they alternate in texture like winter/summer rings do in wood.

 

I accept that there's a very real chance it's not wood, but either way it's a gorgeous stone with those iridescent streaks and I'm still on the "it's wood" side for now 

 

 

[abyssunder]

Could you determine its specific gravity?

[ashcraft]

Looks woody to me.

 

Brent Ashcraft

[Rockwood]

On 3/4/2019 at 10:23 PM, winnph said:

look like they alternate in texture like winter/summer rings do in wood.

To me it looks more like a tropical wood, so perhaps seasonal variation would be a better description. 

[winnph]

2 hours ago, Rockwood said:

To me it looks more like a tropical wood, so perhaps seasonal variation would be a better description. 

 

Point taken! And since this is a beach stone in an area with many different types of geological formations, both along the coast and up nearby creeks/rivers, it'd be pretty tough to figure out what layer it came from and thus the local climate when it formed. Currently it's surrounded by temperate rainforests, though!

[winnph]

13 hours ago, abyssunder said:

Could you determine its specific gravity?

I can't seem to find my more sensitive scale (+/- 0.01g), but with my kitchen scale (+/- 1g) and using cold tap water (so probably more error bars from being too cold and dissolved minerals), the specimen weighs 36g and displaces 14g when suspended, so that would be a SG of just about 2.6 unless I messed up somewhere.

[ynot]

Once again, this piece looks like the layered siltstone that is common along the california coast.

Does not look like petrified wood.

[Rockwood]

54 minutes ago, ynot said:

Once again, this piece looks like the layered siltstone that is common along the california coast.

Does not look like petrified wood.

Much as I hate to admit it,  Tony probably knows what he's talking about.

[Plax]

the vertical grain and laminations are more like wood to me. I don't have any experience with laminated rocks on the west coast but east coast laminated rocks don't have laminae like this.

[abyssunder]

6 hours ago, winnph said:

I can't seem to find my more sensitive scale (+/- 0.01g), but with my kitchen scale (+/- 1g) and using cold tap water (so probably more error bars from being too cold and dissolved minerals), the specimen weighs 36g and displaces 14g when suspended, so that would be a SG of just about 2.6 unless I messed up somewhere.

Thank you!

Its specific gravity of 2.60 (+/- 0.02) match the siltstone's SG.

[Zenmaster6]

8 hours ago, winnph said:

I can't seem to find my more sensitive scale (+/- 0.01g), but with my kitchen scale (+/- 1g) and using cold tap water (so probably more error bars from being too cold and dissolved minerals), the specimen weighs 36g and displaces 14g when suspended, so that would be a SG of just about 2.6 unless I messed up somewhere.

Hey, I realized now that you were in the Puget sound. I also live in the Puget sound, specifically Tacoma.  
I have never found petrified wood on any beaches here (12 years of experience) but I have found petrified woods in siltstones in good marine sediments up by Renton. Good luck!
 

[winnph]

1 minute ago, Zenmaster6 said:

Hey, I realized now that you were in the Puget sound. I also live in the Puget sound, specifically Tacoma.  
I have never found petrified wood on any beaches here (12 years of experience) but I have found petrified woods in siltstones in good marine sediments up by Renton. Good luck!
 

 

Thanks! This was found on the Olympic peninsula oceanside beaches, not in the sound. The geological map for that area lists these as the main layers exposed immediately along that beach, but this is a well-weathered stone so it could've come from elsewhere along the coast or inland, especially if it came from one of the glacial/fluvial deposits:

 

Qad

Alpine glacial drift (late Wisconsinan; Fraser
age)—Deposits mapped as unit Qad may include
outwash, till, and lacustrine sediments. Ablation till
and deposits underlying dead-ice topography are also
mapped as Qad. Drift is mapped where several depo-
sitional environments are represented by deposits in
near-vertical exposures, as along stream banks. Unit
Qad underlies much of the valley bottom adjacent to
the Hoh River, upstream of the Hoh oxbow.
Unit Qad deposits are equivalent in age to mo-
raines of the Hoh Oxbow glaciation mapped by
Thackray (1996).

Mml

Marine clastic rocks, dominantly thick-bedded
lithic sandstone (Lower to Middle Miocene) 

Unit Mml is composed mainly of nongraded, 1–50 m thick,
multistory lithic sandstones and matrix-supported
granule conglomerates. These coarse-grained rocks
are laterally discontinuous and vertically separated by
a few meters to more than 100 m of thin- to medium-
bedded shales and laminated siltstones similar to
those of unit Mmr.
Most unit Mml exposures include five or more ver-
tically stacked beds, ranging from 0.5 to 5 m thick.
Except for rare poorly developed, normally graded
beds, most sandstone beds are massive. However, in-
dividual thick sandstone beds with massive bases and
widely spaced, parallel laminations and (or) parallel
banding developed within a meter of the top are also
present. Both the massive sandstone sequences and
sandstone beds with laminated/banded tops are gener-
ally lenticular on an outcrop scale, although map pat-
terns suggest that some larger packets are tabular.
Dish structures are present in some outcrops, and
loading features are present on some bedding planes.
Rare tool marks and current lineations generally trend
northeast or southwest. A few Bouma sequences have
been observed in the Kalaloch Creek basin.
The sandstone and granule conglomerates are
lithic to lithofeldspathic arenites (Dickinson, 1970).
They are medium- to very coarse-grained and moder-
ately to well-sorted. Most massive or laminated/
banded sandstone beds contain rip-up clasts or intra-
clasts of mudstone, very dark-gray siltstone, and (or)
tuffaceous siltstone. These clasts are generally tabu-
lar, range from 0.3 mm to more than 30 cm in length,
and are oriented parallel to bedding. Many of the tabu-
lar rip-up clasts taper to very thin, fragile edges. They
are gray, dark gray, or olive gray and weather tan or
light gray.

Mmr

Marine rhythmic thin- to medium-bedded sandstone
and shale or slate (Lower to Middle Miocene) 

Unit Mmr is a monotonous sequence of gray, very fine- to
medium-grained, feldspatholithic to lithofeldspathic
sandstones and very dark gray siltstone and shale or
slate, much of which is rhythmically bedded (Rau,
1979; Tabor and Cady, 1978a; Weissenborn and
Snavely, 1968). The sandstone to siltstone plus slate
ratio is generally greater than 1. Bedding characteristics are most useful for identifying this unit. With rare exceptions, bed thickness ranges from laminations to less than 50 cm and averages about 10 cm. Most of these rocks are parallel bedded with little or no variation in thickness observed at outcrop scale. Basal and upper contacts are generally sharp, but a few sequences are composed of a basal sandstone bed that grades upward into laminated siltstone and (or) shale. Most individual sandstone beds are laminated.

Unit Mmr varies from gray, brownish gray, or olive
gray to very dark gray. Sandstone beds and lamina-
tions are lighter colored. Detrital muscovite and very
dark gray, platy rip-up clasts are common in the sand-
stones. The sandstone and siltstone beds have blocky
weathering profiles and commonly form a colluvium
of 2 x 2 x 4-cm blocks. Weathering colors are gener-
ally medium to dark gray, yellowish red (5YR5/8 to
7.5YR5/8) (Munsell Color Corp., 1975), medium red-
dish brown, or a distinctive reddish yellow (7.5YR6/
8).

 

Qgdc

Glacial and nonglacial deposits (Fraser age or
older) These deposits consist of stratified fluvial
cobbles and gravel exposed in sea cliffs of the marine
terraces near Kalaloch Creek. Unit Qgdc deposits are
generally oxidized to 1–3 m and capped with 1–2 m of
loess. They are probably reworked from units Qapo
and Qapwo2 and alluvium from Kalaloch Creek. De-
posits are gently dipping and laterally continuous,
suggesting deposition in a beach environment and re-
working by coastal waves. Some cut-and-fill struc-
tures and foreset beds exist.

[Plantguy]

I suppose it could be a siltstone but that alternating elongated/splintered looking textured pattern in the banding in the upper right of the 1st photo suggests to me that something else is going on in the those layers and its not just silt sized clasts so i'm leaning more towards the wood hypothesis at the moment. Its not a carbonate is it? fizz test with vinegar? whats its relative hardness? scratch with a knife?

I wonder if some closeup/scope work might show some vestiges of possible woody structures pores/bundles? Its sure too unique/pretty to cut/take thin/polished sections of which would confirm an ID. 

Very Cool find! 

Regards, Chris 

[Wrangellian]

I'm not certain but I would bet on the side of wood. It's got a somewhat fibrous look which I couldn't account for in regular sedimentary rock.

Also, the black color does not detract from being wood: I have chunks of wood from the local river here (upper Cret.) that are black (coaly) but still retain a clear wood grain.

[Scylla]

Looks like wood to me. I agree with most of what has been said above on both sides of the issue, but if I have to choose without a hand loupe close-up, then my bet is on wood. If you have a loupe you might be able to use your cell phone camera with it to get a highly magnified view.

[Rockwood]

@ynot Can you show us a photo of the siltstone for comparison ?

That side of the scale is looking a tad light. 

[ynot]

6 hours ago, Rockwood said:

@ynot Can you show us a photo of the siltstone for comparison ?

That side of the scale is looking a tad light. 

Sorry, no I do not have a sample of siltstone to match this one.

8 hour drive one way with hours on the beach.

Not something I normally keep.

[Rockwood]

2 minutes ago, ynot said:

Sorry, no I do not have a sample of siltstone to match this one.

8 hour drive one way with hours on the beach.

Not something I normally keep.

Now that's disappointing. A mere 16 hour drive is going to keep you out of a good argument.  

[ynot]

3 minutes ago, Rockwood said:

Now that's disappointing. A mere 16 hour drive is going to keep you out of a good argument.  

 yep, it sure is!