Tim wrote:

One piece has grain and rays like white oak, but it is very dark; the color
of white oak, but the darkness of walnut. It also has numerous very small
pockets of decay.

Quite possibly.

I use a fair bit of SW English brown oak. Here's some (no finish, other
than oil and wax)
http://codesmiths.com/shed/things/boxes/wedding/
http://codesmiths.com/shed/clocks/stickley_nixie/

There's no reason why brown oak is particularly rot prone, and it was
used for hard-wearing flooring for many years, when darker oaks just
weren't fashionable for furniture. Nowadays this recycled flooring
carries a premium price! One thing you do find though is that the
poorer grade boards are striped with brown, not solid. I believe that
you're not looking at the fungus itself, but rather the byproducts of
it, carried up the trunk. If this striping is attractive it's sometimes
called "tiger oak" (sometimes quartersawn heavily rayed oak gets the
same name). If it's unattractive, it's called firewood.