What is a black locust tree?

We grew a black locust tree in northern Vermont, from a seedling in a cup given to us by some tree foundation. It grew lightning fast and was very beautiful. The foliage seems to resemble ash tree leaves, very green, and the trunk and limbs are very black, for a striking contrast. There are small thorns. It develops red seed pods. We saved seeds from the pods to plant in the next house and, again, grew very very fast. We never had problems with borer beetle but we planted it near the house in an empty field each time, with no other trees nearby. My understanding is that early settlers used the wood for fence posts and tool handles, etc., as the wood is supposed to be very dense and durable, though i've never worked it myself. A nice alternative to the typical maple, beech trees, etc...