I agree with Paul, it looks like teak and since teak was a popular wood for parquet floors that seems like a strong possibility.
If it has a slightly oily feel that would confirm it. The hardness and brittleness could, as you suggest, come from years of exposure to footfall and sunlight so it is hard to be certain
Anyway, whatever it is it makes a fine pen and although I am of the school that believes that the clue to the best shape for slimlines is in the name I think the curves on yours flow nicely and make an attractive pen. Clearly some thought has gone into the design.