Shocked rock = breccia ?

May not require anything as earth shattering as a comet impact. How about freezing, earthquakes/tectonic pressure or just plain ol water? Maybe Mel has some answers to such mysteries.

Re wood breccias, I too doubt anything to do with comets. I think most likely a combination of pressure stress as the petrified wood was compressed between layers of sediments and water intrusion and weathering that caused most of the fracturing, which was thereafter resealed with silica from those overlaying layers of old marine sediments. This compression is often seen in recovered full rounds here in Texas which are no longer rounds like at Petrified Forest but rather compressed ovals or flattened hunks. This especially is apparent in palm rounds most all of which are no longer fully round.

Some of the brecciated effect may just be due to partial decomposition of the actual wood before mineralization too. Texas specimens often show evidence of full decomposition before mineralization ( limb casts) or partial decomposition by fungi or bacteria. ie pocket rot wood. I suppose in that case, the actual wood might be mineralized with opaque jasper replacing the unrotted sections and clear chalcedony filling the voids. Most the famous shrinkwood / hexagonally fracture petrified wood, seems from the patterns, to have been broken and resealed after petrification. Scott addresses this process well in his internet paper. Just Google Hexagonally fractured petrified wood. This wood, by the way, is much younger creationwise, than the big comet strike period in the late Cretaceous. Think its mostly like only 20 million years old or so.

As for non wood conglomerates, that's a lot tougher, as in the Rio grande gravel, there are certainly a lot of old rocks, so there could have been a lot of different stresses shattering them over the eons, probably including the big ole comet. Could have started as an almost concrete like conglomerate of caliche and hard fragments from multiple sources and then had the limey parts dissolved away and replaced with silica. This is kind of illustrated when you cut some of the crappier breccia which is not fully infused with silica and still has cement like granular stuff in some of the voids.....Mel

WOW! That's a nice one!

Yep, that's classic hexagonal fracturing. Not always perfect hexagons but very geometric. Lots of that in George West region of Texas and not part of the plant structures, though remains of plant vascular system can often be seen within the fractured areas. Again, the article by Scott on this wood is very informative and well worth a read. Couple of classic George West examples:

So much breccia on the Rio. It just buffaloed me. Breccia that looked like some God awful forces worked on it.
Extreme force understandable, but it looks like high speed impact type forces to me. Like above rock.
As if the earth was a meteorite field at numerous times in it's past.
Some look as if re-healed several times over. i.e. long periods of time between damage.
snowmom has displayed photos of impactite from that big comet in S Canada. Not much different looking than much of the Rio breccia.

HFPW, shrink wood, pocket wood all make sense due to organic matter altering in many ways after listening to above conversation.

Freeze shattered, makes sense. Certain it got very cold

Cut a few slabs

Now this one was shocked just a bit! pETRIFIED WOOD from the Stinking Water mountains of Oregon.



photobuckete sucks!!!

Looks to me like a metamorphic . metamorphosed sedimentary rock .

i think silicified sedimentary rock is what it is now. see any fossils in it? . the silicication can distort the fossils and often obliterate them leaving remnant patterns .as i look at it now,it looks like a moss type agate possibly after limestone or a fossil limestone ...