Down in Florida, there is a pine, wood, that has been used in the early 1900's through the fiftys, and some of the sixties. It is called Dade County pine. Being it was in south Florida, and grew on land that was on old coral beds, and hence had absorbed the minerals. It is as hard as oak, and when you try to cut it with a skill saw sparks will fly, making you think you hit a nail. When you drive a nail in, you are not going to just pull it out, if you bend it. You will either work for 20 to thirty minutes trying, or just wring the end off, and try another nail near it. I would love to see how in the hell they cut and milled those trees, back then, since they did not have carbide tipped saw blades! Houses made with that pine are still standing, and is very rot resistant, and very strong. Usually heart wood was used. It is very heavy. It is a rich reddish orange color, and sometimes just looks like yellow pine. But once you try to cut it, or drive a nail into it, you will know immediately what you have.
Wayne