I bought some way back when, and it was amazingly hard.
There was another kind of lead that was used to cast full sheets of type, although I can't find it online in any references. Type was punched into heavy fiberboard. Molten alloy was injected into a mold that was faced with this punched sheet. the result was a round printing press plate.
This wasn't linotype metal, it was softer and brittle. Any type metal that you find that's in full sheets should be taken with a grain of salt.