I asked around to see if I could figure out where the rock came from (a lot harder than it probably should have been to determine the source), and it appears to have come from Arizona but that was all the detail I could get.
I pulled a bunch of rock from other tanks and cleaned it to see if I could find similar formations/coloration and sure enough, many other pieces of black lava rock from several sources showed the same coloration. Since I havenít had any issues with the other rock, Iím not too worried about it but just to be safe I am going to bath this rock in a mild vinegar solution for a few days to see if it has any effect.
Once thatís done, Ill soak the rock in distilled water for a few more days. If Iíve still got any doubts at that point Iíll send a sample of the water to triton for a full work up.
If nothing else, it will be interesting to see what, if any, minerals are leeched from the lava rock. If anything did leech, My guess would be mostly sulfur, silicates, iron, and magnesium with possible trace amounts of all kinds of metals like aluminum, nickel, gold, lead, etc.
Iíve used black lava rock in everything from reef tanks to discus tanks and never noticed any ill effects from it, but then again I donít know that I ever would have made the connection if there had been issues. Still, a few days in a mild acid solution just to be safe canít hurt.
Experience: worked in fishroom of Eddies Aquarium in Albany all through college, 20 years of keeping reef tanks, planted tanks, and dart frog vivariums.
Current/in-progress tanks: 20 gallon hi tech tank in office, 120 gallon nature/tetra aquarium at home.
Philosophy: work with what youíve got, and make choices based on the conditions that easiest for you to maintain over time.