"There are two very simple ways to test rock to be sure they are safe for your aquarium. The first method uses Muriatic Acid (MA). This can be found at either a swimming pool supply store or possibly a hydroponic supply store. To test any given rock, put a few drops of MA on the rock, wait a couple of seconds and watch for bubbles. If bubbles are seen, this rock is NOT safe. Distilled white vinegar can also be used in a pinch. The MA test is more accurate though.
Safe Rocks:
- Crystalline Quartz
- (Rock Crystal, Amethyst, Citrine, Rose Quartz, Smokey Quartz)
- Granite
- Jade
- Lava Rock
- Microcrystalline Quartz
(Jasper, Agate, Chalcedony, Sard, Carnelian)
- Onyx
- Petrified Wood
- Quartz
- Slate
Unsafe Rocks:
- Coal
(Commercially harvested coal is treated with an oil by-product to reduce dust)
- Coral
- Dolomite
- Fools Gold
(or any other rock with metallic veins--Acid Producing)
- Fossils
- Limestone
- Marble
- Sandstone"