I don't want to sound like an expert,,god knows we learn new stuff every day.
Desert (sonora) Ironwood only grow below 4,000 feet and is exclusive to that area (71,403 sq mi ) the wood is so dense it will not float in water, the oils in the wood seal it naturaly and most Ironwood trees live over 2,000 years.
Tre extreamly dense matrix of the grain structure will not allow anything to permeate into it. The oils it contains prevents it from decay even left out in the elements for years
Skip (Phoenix Arizona/Ironwood Rd.)
P.S. the oxidation of the surface of the wood turns it black