Or is this common?
First, a bit of backstory on how I got the pet wood this is from.
A neighbor of mine lives/lived down at the end of the alley. Rockhound & rock cutter. I've gotten to know him a bit & he's given me a few small pieces here & there. He recently & suddenly moved out of the house & a couple weeks later a contractor was tearing it down. They are currently building a new house on the spot. My neighbor was going to try to catch me before they moved out to tell me to grab whatever rocks I wanted from the yard (I ran into him yesterday at the local parade), but wasn't able to with me working nights. Turns out he had a largish pile of rocks in front of his shop that basically got bulldozed & probably buried. He told me if I saw any of them, to go for it & take them home. I found one... a chunk of petrified wood that may be partly agatized and/or opalized, not sure yet. I'll get pics of it later. Turns out it weighs 31 pounds.  It mostly survived a fight with a backhoe, taking a bit of damage, but is mostly intact. Small pieces came off while cleaning it up & I saved some of them. One is sort of giving me fits. First pic is of another piece that came off close to the one in question, end shot showing it to be pet wood. Pic 2 is with the Dino-lite leds on, pic's 3 & 4 is with them off, but using a small led flashlight. Pic 4 is with the light at a slightly below angle. All 3 are the same magnification of 50 x & in same position. Pic 5 is of another section to the left of the others. Not sure what to make of these. They sort of look like worms. 

Happy Labor Day to you as well!
Could be prehistoric gummy worms maybe.. Thing is, these are on some of the surfaces. It's going to take some doing to get pics of the entire chunk. I just passed the middle of 9 straight nights at work, 4 more to go, then 2 off, so I'll try to get pics of it in the daylight this weekend. I'm just glad I didn't drop it on my foot. 

Well, yes, it has probably all been replaced by silica/chalcedony at this point. The bright green UV reaction is common for chalcedony.
As Phil Collins would say, Sue-Sue- Psuedomorphs!

But your 'worms' could have formed as Aragonite, Calcite, or other minerals before being preserved in Silica.
Here's a good site for research and general perusal. You'll like the pictures, too!
http://agateswithinclusions.com/