For any rocks you are considering, one general rule is to put a few drops of white vinegar on them...if the vinegar fizzes and bubbles up, then the rocks are calciferous, which means they could change the ph and hardness of your water, which could stress fish...if the vinegar does not fizz, they should be safe to use
Of course, clean any rocks you are going to use with some hot water and a brush before you put them in.
hope this helps
10 Gallon: 8 Platys, 2 Guppies, Snails, some RCS, and plants
40 Gallon Breeder: 10 Rosy Tetras, 10 Red & Blue Colombian Tetras, 10 Marbled hatchets, 7 Pristella Tetras, 6 Sterbai Corys, 1 Ancistrus "Rio Tocantins", 2 Re-homed Platys, plants and DW
"Don't cry because it is over; smile because it happened" --- Theodor Seuss Geisel