Rock that is calcareous, meaning composed of minerals like limestone, marble, and similar primarily-calcium rock, along with coral and shells, will very slowly dissolve over hundreds of years. Such rock is usually found in the earth, and water that flows over or through it picks up the dissolved minerals which is what makes the water "hard" to some degree. If you have calcareous rock in your aquarium, it will still be slowly dissolving long after you and I are no longer here. There is a test to determine if rock is calcareous or not. This involves using a strong acid with a few drops on the rock, and the degree to which is fizzes tells you it is calcareous.
Rounded "river rock" which you can buy in landscape supply places and quarry outlets should generally be safe as it will usually be granite.
The intensity is likely OK (maybe even too bright, but floating plants can help with that) but what is the spectrum? Is there any data on the unit, the package, or the manufacturer's online site that gives the Kelvin for this light? Anywhere between 5000K and 6500K is ideal light.