What kind of rock is this?

Farmerman, our resident petrologist, will be along shortly to answer your question. Or Rosebone.

It looks a bit like petrified wood but the location seems unlikely for that. If you look closely at it do you see any wood grain? Is it crumbly or rock hard?

It proably IS "coalified wood" from the Tertiary depoits in the center of DC. The geology of our nations capitol is quite unique. There are a whole bunch of pot Cretaceous fults that separate the Peidomont terrains of the North and West. This has created a "Fall Zone" of lots of deposits that are of Tertiary and Quaternary ages. The most famous are the Aquaia and the Calvert Formations which contain near shor and prograding deeper water units as the area rose and fell belwo sea level. SO the layers of these carbonized woods are common.
If you want to know more you should get a copy of
USGS Survey Circular 1148, which is a popularly written publication of the mapping of the Baltimore and Washington Areas
That's why you can go out to Rock Park and the Zoo and be in the middle of very hard schists and gneisses and then as you come southeast, all of a sudden you are in these recent sedimentary deposits full of fossil sharks teeth, or coiled shells and even terrestrial reptiles and ,later, mammals/
Its a real dogs breakfast and if it weren't for all those damn Federal buildings there would be some good fossil hunting

What is "Coalified Wood"? I haven't heard that term before. Is it like "young" petrified wood or something?

That reminds me of "The Creek" when I was a kid. As I may have mentioned before, I grew up in Holmdel New Jersey and there was a creek which ran through the neighborhood. We used to go there all the time to find fossilized sharks teeth and other things.

We just called it "The Creek", but it is actually named Ramanessin Brook which is near Big Brook.

Examples of what we saw and of the area we played in can be seen here:

http://www.fossilguy.com/sites/bbrook

We found hundreds of these:


http://www.fossiling.com/ramanessin.html

petrified usuall refers to the actual chemical replacement of wood by some other chemically deposited rock type (like a type of crypto-quartz [jasper, agate,chalcedony etc]).
Coalification is a term of art used by the AGI to mean that the wood is gradually (through compression etc) converted to a pure carbon .Its actually a form of slow "burning".
weve got a tone of other words that mean the same thing but, at least to me, are just tying on fifty dollar words to simple processes.
Colification has been substituted for vitrinization,fusinization,carbonization etc

Whenever someone new does some studies on a "cannel coal" "bog coal" or peat, they always want to insert some new term or two and it gets downright annoying whenever these words become accepted in the mainstream. SO ,"Coalification" is a simple term that sort of explains the source and methodology of production of the fosil charcoal under question.


The really fascinating thing about Washington DC is thae very sudden fault line breaks in the geology from NW to SE.
Its a true "fall zone" where our early cities were located because of the steep topo breaks that allowed water mills to be located without digging long mill races from up river (like they have to do in streams in the Midwest.

there was a similar site for the CLVERT CLIFFS in Md. The Calvert cliffs are the type of formations that also underlie DC.
I found a CARCHARODON MEGALODON tooth while diving off the cliffs many years ago. I was actually fpear fishing for flounder and saw this huge tooth just kying on the bottom of the bay.

Do you still hqve your shark tooth "Stash" from when you were a kid?
I have my Megalodon tooth somewhere around here.

Sadly, I lost the bulk of my stash many years ago. At one point I had hundreds of them all in a plastic baggie. Some of the Goblin Shark teeth were almost 2" long and were probably the biggest ones found there by us amateur kids. All I have left now is 4 or 5 small teeth which I retrieved as an adult years later when I went back to New Jersey for a visit.

About 15 or 20 years ago I was on a business trip in Princeton and I decided to drive back over to Holmdel to see the old neighborhood. When I got there I found an entrance to the creek (just as I had remembered it) and climbed down into the mud banks (still wearing my business suit) and was able to find a few teeth with just a few minutes of looking. Those I still have. But the really big ones from my childhood are long gone.

See? What'd I tell you, Rock? Farmerman and Rosborne are our two experts on this subject. They'll always answer your rock questions if you post them here.

the answer to the last rock question is STeven Tyler

And here I thought it was Frank Zappa.

I appreciate your confidence in my opinions, I really do. And I'm probably not completely off the mark in most cases, but to be clear, I'm not in Farmerman's league when it comes to Geology knowledge.

Ros that was my first guess too, petrified charcoal