I would not use it. It is definately a seemintary typ eof rock. The shiny thigs are mineral deposits, usually a metal. Sedemintary rock is generally soft, and is formed by deposits, generally from water movement. this would stand to reason seeing that you are from southern Texas. Generally, the rocks you want to use are those that were formed under pressure. Granite, quatrz, slate, and lava type fallout. All these are fairly inert and safe for the aquarium. Incidently, vinigar is not a very strong acid and it is better to test things with muratic. You can get it at most hardware stores..