My informant has lived on the island of Hawaii his whole life. He currently works at the Hawaiʻi Volcanoes National Park. He first heard of the superstition when his parents would complain about the increasing amount of tourism to the island. They would justify their discontent by acknowledging that all of the tourists who would return home with volcanic rock would be stricken with bad luck.
At the national park, my informant has been taught, and is expected to know, the details of the superstition. Apparently, the volcanic goddess, Pele, curses visitors who return to their homelands with a lava rock. At the national park, they frequently receive packages which contain lava rocks that people have taken and wish to return because of their bad luck. They expect that by returning the rocks, their luck will change for the better. The worst instance he has heard of was a man who was laid off of work and broke his leg in the same month. He believes the superstition was created by native Hawaiians trying to discourage tourists from disturbing the landscape. He has never left the island with a volcanic rock before, so he doesn’t have any firsthand experience with the curse.
In my opinion, the lava operates as an item the tourists can blame their misfortunes on. Then, whenever something goes wrong, they think of the lava rock instead of brushing it off. Then the tourists feel like they have to free themselves of the burden the rock has put them in. Also, I have heard of how much the native Hawaiians hate tourists, so it’s likely this superstition was started to discourage tourist activity. Also, this makes sense because tourism to Hawaii has only become popular in the last century. To tie an ancient figure like Pele to a more modern practice makes it evident that the curse is not genuine and the native Hawaiians just don’t like tourists taking pieces of Hawaii home with them.