Testing Rocks

[DonkeyFish]

Ok, so I went back and found some posts about what to do to test rock for aquarium use. I found a new construction site with OODLES of freshly dug up rock and pilfered through the other night.

Is there a general consensus about pouring vinegar over a rock to see if it bubbles as being sufficient? Just regular white vinegar or a certain kind? And what, exactly, is that going to tell a person? I know Limestone is no good for a tank unless you want to make a mini rift-lake with lots of hardness and such, but why is that?

And what else would make a particular rock unsuitable for aquarium use?

I know, I totally should have paid more attention in Earth Science class. That was my freshman year in High School though... I had WAAAY better things to be worrying about! And I'm pretty sure the topic of "which rock can go in with your goldfish" never came up... although maybe then I would have paid more attention!

TIA for any help!

[DelawareJim]

Pouring vinegar basically just tells you if there is calcite in the rock. It bubbles as the acid in the vinegar reacts with the calcite in the limestone.

Basically you want a hard rock, the harder the better. This is generally measured using the Mohs Mineral Hardness Scale. If I recall, Talc is softest with a rating of "1" and Diamond is hardest with a rating of "10". Also try and stay away from rocks that flake easly like slate and shale as they often flake off sharp edges that may injure the fish.

Stay away from shale as it contains oils that will foul the water.

I would guess that most rocks in the Piedmont (eastern VA, MD, DC metro area) found at construction sites are probably native quartz, granite, gneiss, basalt, and their relatives that for the most part are hard, and inert type rock.

Cheers.
Jim

[Cavan]

Vinegar is frequently not strong enough to get a reaction, so you really want something stronger like concentrated Acid Buffer.