illegall??? depends on the state, they all may vary, ethical. i don't know, but practical???
if i recall right, sand off hawaii si lava soot?? i would prefer to use aragonite, although some people have had luck with lava rock, it can and does have minerals in it, some of which may possess a problem for a marine aquarium(some may not, depending on the locality and what minerals theere would be), and another note, to overnite a gallon of ls from hawaii to michigan i would think would have to cost about 20-30$ dpending, one bag of ls and a bit more than a gallon is @30$ in most areas anyhow
but if you do, the best thing to do is go surfing and check the local laws, when i went to cozumel, one side of the isle, it was illegal and the other side was not, and you are only talking about a couple of miles(maybe 3)
HTH