djbrist

I purchased some dec. rocks in bag from Walmart's pet aisle, threw away tags, they were really pretty with striations of lighter colored minerals thru darker. These all have a very polished sheen but I can mar the coating witha file/knife. Question? what is this coating if any, and should I try to remove it or is it "protecting " the water from leached minerals. I did the acid test on the stone over the polished and marred sides seperately with no reaction. Hoping our resident Geologist (prairielily) comes around, but I'll take an amatuers advice though wink

Thanks, Dave

prairielilly

whoohoo I'm getting a reputation? hopefully I can help. It's hard to say (can you post a picture?) but I'm guessing some quartz pebbles, I've bought similar at Wally before, but then you wouldn't be able to scratch it with a knife...when you did that, were you able to remove the mark it left with your finger, or does it stay? if you can remove it with your finger, the knife came off on the rock instead of the other way around. If it did leave the mark alone, you MIGHT have a limestone/dolomite - vinegar's a pretty good substitute, but isn't 100% accurate (muriatic acid isn't something ppl keep in their kitchens though).

The polished sheen is (likely) from going through a rock polisher. IMO nothing's been added to the rock.

Another test: find a ceramic mug (or plate, whatever) and flip it over - usually the bottom 'rim' is unglazed (looks dull, feels rough). Run the rock over the unglazed part and see if it leaves a mark there. White dust counts too!

Pictures!

Still thinking (I like rock q's ): dark with light minerals, soft rock...could be marble, or shale, or a pelite with quartz veins...Marble's made of calcium carbonate, but from other threads here it doesn't seem like the leaching of calcium minerals is really anything to be worried about as wc's remove it usually. If anything's irridescent or purple or metallic looking, THAT we need to clarify.

Thanks for thinking of me on this, this is fun!

djbrist

Ty, I'll try pix tommorrow, but yes must have been file left on rock, very hard!, the feel left on my fingers after handling them, kinda like waxy?? You got me with the muriatic, I do use it in my work, to patina copper, and prep stainless steel for soldering. Will also try ceramic tommorrow, I'll post results and pix then, thanks again.

prairielilly

No scratch, likely quartz? if you can get to that acid, try some on the white parts - they may be white quartz or white carbonate. About the waxy feel, hmmm...no rocks are made of wax I wonder why a store would put a coating on rocks? You could always boil them just to be safe.

djbrist

Yes to the boiling, no to the scratch on the lighter areas, must have been the file rubbing off on rock, and wax could very well have been leaching from MY fingers as I expose my hands to some nasties daily, rock IS harder than ceramic in mug, and no reaction with acid anywhere...

here are pix

I was just wondering if the "polishing outfit" would use any types of coatings to swindle us lovers of rocks.

thanks for your feedback, It is great to have such a resource

Thank you again Marsha!

Dave

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Shawnie

cant help like marsha can but I have some of those in my tank...great additions

≈ D ≈

djbrist

thanks guys!

prairielilly

I think that you've got sandstone/shale pebbles - I'm betting you can't see any grains in them, and if you can the tan parts have bigger grains than the black parts, and possibly there's some fossils in there? little round things, linear tracks? I think they're originally from a beach, not like where you'd walk and get some sun, but deeper in the water where the coarse beach sand gets mixed with shale as the basin gets deeper, where it's nearly ALL shale. Then a long time later the water's gone and the rock sticks out somewhere at surface - we call that 'outcrop' - and bits are eroded off by water and end up in a river, giving them that nice rounded shape. Certain minerals would have left a streak on the unglazed porcelain, good that it didn't. From the hardness test they've likely got quartz in them or something harder (and not much is) which is common in beach sand, and from the appearance it's either something that was originally a bedded rock, like the deeper beach rocks I'm mentioning, or has been metamorphosed and now has a lineation. Or both! This is what geologists get to do, look at rocks and make a 'best guess' to figure out their life stories (and then the lucky ones get to go treasure hunting for oil and gas!) I should stress though that I really can't be CERTAIN SURE from this information, if I were doing this at school or professionally I'd have to make a slide out of it and look at it under a microscope, or at least look at the rock under magnification. Can't do all that, so this is what I DO know: either of those possibilities is likely made of the same stuff, is inert and therefore completely safe for an aquarium. I don't see anything to indicate any heavy metals/minerals that could leach out and kill fish. I'd be perfectly fine with putting them into my own tank (they look really nice too!)

So far as the possible waxy coating - I'd boil them. Won't hurt the rocks! Polishing doesn't add anything, it just 'tumbles' it (sort of like a glorified clothes dryer?) until it's shiny. Kind of like ppl who have a 'granite' kitchen counter (most aren't granite, but oh well) - it's been polished, but in a different way. The 'raw' rock is dull looking.

One last test? see if a magnet sticks to it.

that was fun! thanks for letting me play!

djbrist

Last test= no magnetic polarity seen, so no iron and such metals? Great though, going in the 29 gal for looks of dark substrate, you'll see soon when its cycled then stocked and I'll post pictures.

THANK YOU!

prairielilly

You're welcome - this is fun for Marsha so thank YOU!

(no magnetic inclination = no magnetite or hematite, iron-bearing minerals that could potentially leach. Also [sort of] confirms my hypothesis )

Looking forward to the pictures!