If it's lava rock, it should be just fine, and generally won't leach anything.
Most lava rock is basically the same mineral composition as basalt, just full of bubbles and cooled to quickly for visible crystals to form. Not real sure what type you have, it looks a bit lighter then typical basalt. Probably something more like granite/diorite or something. Nothing that can really leach out of it.
About the only exception I can think of is if the lava rock was gathered from a carbonate-rich area, and some of the carbonates had washed over/deposited on the lava rock, but that would probably be visible.
It might be worth soaking and scrubbing with a brush if it looks dirty, but other then that, should be good to put in the tank.