charzar-g

Hello all
I have yet another question for all you intelligent peoples!
When i went to yorkshire for the week, (just got back) We went to the beach, and it was a sandy beach, but there were loads of these big pure white rocks, they were smooth, but slighly holey, and i was wondering, does anyone know what type of rock this is?
And is it safe to use in a freshwater tank and a saltwater tank? Because i took a few peieces :P
It also made a little bit of white powder on my hands when i rubbed it, but its not chalk :P

Llama

White rocks..

Limestone? If its limestone it'll dissolve in water slowly...

Grab an acid (even vinegar) and drop some drops upon it. If you hear fizzing, then its limestone (calcium Carbonate) and not good for aquarium use.

Otherwise just wash/boil them well, then leave overnight in a bucket of water and then check the water parameters

Jonah

If it was Yorkshire its Limestone, some of the largest chalk uplands in the UK are in Yorks

prairielilly

Yup.

Any fossils? Feel free to post a pic? then could make a positive ID (I'm a geologist)

charzar-g

thats a darn shame if its limestone, and prairelilly, i'd be happy to post pictures, but I have no idea how =[
Do you?
And i will do that vinegar test Llama

charzar-g

okay, sorry to double post, but it turns out that the rock IS limestone, it fizzled a little when i put the vinegar on, so i guess thats a 'no go' for the tank, but i also picked up this dark grey rock, at first glance you'd think it's slate or something, but its not smooth not shiney, i put vinegar on that too, no fizz, anyone know what it could be?

Llama

Well our resident geologist up there could certainly help.

Limestone isn't good for aquariums because it decomposes slowly in water, and messes up on the hardness and everything. The fizzing just so as you know is

Acid + Carbonate -> Salt + Carbon Dioxide

ADDED: To post pictures just take the picture and put it on your hard disk. Then open advanced posting mode (ie don't use the quick post) at the bottom there is a 'manage attachments' button. Click it, upload your file and you're done.

Jonah

They Grey is probably Slate, where abouts in Yorkshire were you when you picked it up and I would be able to tell you more certainly

Just as an FYI if you were iin the Whitby / Sandsend area the commonly found coastal rocks there are Sandstone/mudstone, pyritic shale, some Jet and limestone / flint in inland areas

prairielilly

Grey rocks could be anything, many rocks are grey. Dolomite, shale, slate, sandstone, limestone....(some rocks are combinations of dolomite and limestone, and won't fizz in dilute acid until you scrape some off into a powder and put the acid on that).

Do you see any fossils? is it shiny or dull? is it flat and rectangular, or rounded and lumpish? does it appear to be made of many small grains, or not? try scratching it with a) your fingernail, b) a penny, c) a steel table knife, let me know the results.

Love to see a picture!

Jonah

Just for you Marsha that stretch of coast is Jurassic and you cant walk down the beach without falling over an Ammonite fossil.

prairielilly

...ooohh I wanna go see...

charzar-g

No fossils, dull, flat and rectangular AND rounded and lumpish... (i'm not good at describing ) And it does appear to be small grains i think :/
I'll get a picture for y'all hang on
*runs off with camera*

charzar-g

okay, i got those pictures ^^
Annalise away!

Attached Images

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	S5030834.jpg (289.9 KB, 91 views)

charzar-g

I'm sorry my camera isn't too great, but i hope you can still see it clearly ^^

prairielilly

Looks like sandstone to me (near as I can tell w/o holding it) which would mean it's safe for your tank check: you said it did NOT fizz? even if you scraped some off into a powder first? and did anything scratch it? If it's dolomite (I don't think it is from the look of it) it will fizz when you powder it first, and a knife will scratch it but a penny won't (or really slight). If it's sandstone, none of those will scratch it and you won't be able to powder it.

Edit: the small amount of white stuff is likely calcite (calcium carbonate) but the amount is so small I really wouldn't worry about that.

Thanks for taking the trouble - analyzing rocks is fun for Marsha

charzar-g

Thank goodness its safe!!! ^^
I only thought sandstone came in...well....sand colour :/
You learn something new every day (Y)

Thankyou!!

prairielilly

No problem but DO do the scratch test just to be sure.

Sand(stone) comes in all sorts of colours - red, tan, white, yellow, grey, black. green...really depends on what it's made of and what's holding it together. Most of the sandstones I deal with in the oil industry are grey actually, too bad that doesn't necessarily mean there's oil or gas in them

charzar-g

okay, i'll do the scratchy test, if its sandstone it will crumble and if it doesn't then its.................... :/

charzar-g

okay no crumbly ness or anything coming off it at all :/ Can i upload a video to this site? :/

charzar-g

okay i've just tried to upload a video but it won't let me. soooo idk :/
Shall i just risk it and throw it in the tank? (not literally)

prairielilly

Take a steel kitchen knife (preferably a DULL one you don't care about scratching) and use it to try to scratch the rock. If steel comes off on the rock, pick up the rock and use it to try to scratch the knife. If it scratches the knife, it's harder than steel and is likely sandstone, as sandstone is (usually but not always) composed of quartz which is harder than steel.

If when you used the knife to scratch the rock it left a mark (a cut, not a grey line - that's steel coming off the knife - run your finger over it to see if you can rub it off) then take the knife, lay it sideways and try to scrape off a bit of the rock into a powder. If you can do this, put some vinegar on the powder and see if it fizzes. If it does, you have dolomite (calcium-magnesium carbonate) and while more stable than calcite (limestone) it will still affect your tank's pH and hardness. If you can't get the powder but can still scratch the rock, or can get the powder but it still doesn't fizz, you've likely got a mixture of things, most likely NOT any dolomite, and it should still be safe for your aquarium.

Geology 101 in two paragraphs or less....

charzar-g

Is lost :/
Okay I'll get a knife, and try to scratch it, if it doesn't work, i'll scratch the knife with the rock?? Did I get that right?
And if it makes a powder, put vinegar on the powder, and if it fizzles, its bad for the tank?

prairielilly

Yes, all correct.

Which part are you lost on?

charzar-g

okay, the knife couldn't scratch the rock (made a little white line what just brushed of with a finger) But the rock could scratch the knife, so that means its sandstone and its safe to use??

prairielilly

Yup We can stop there, the rest won't be necessary. If it were limestone or dolomite the rock would NOT scratch the knife.

Geology lesson over. Enjoy the rock in your tank

charzar-g

thankyou x100
I'm so glad I posted this question and didn't just go ahead with putting in all the white rock i found

prairielilly

You're so welcome!
Me too, I love rock questions!

prairielilly

I was thinking about this, the ammonites would be from the chalk. Is the chalk Devonian? (is it the 'white cliffs of Dover'? is so then it is I think but I'm a lot more familiar with my own continent )

Jonah are you a fellow geologist? a rockhound perhaps?

Edit: nope I'm wrong ammonites are Jurassic or Cretaceous! I was thinking gastropods in Devonian limestones...ah well.

Nate McFin

Why not put some water in a bucket...leave it for 24 hours.
After 24 hours test the PH (and KH if possible)
Put the rocks in the bucket after testing the first time. Test again over a period of a few days. If the PH raises you have your answer.
Also the nitrite test solution from an API kit is Hydrochloric acid and will "fizz" a little better than vinegar which is a weak and diluted acid.
If it does Raise the PH it may still be usable depending on your current water params and what type of fish you will be keeping.

prairielilly

The tests I was advising ARE scientific tests, regardless of how simple they are. They are the exact procedure I would go through with any rock of unknown composition I wanted to identify. When I taught labs in introductory geology this is exactly what we taught students to do.

The hydrochloric acid will work just fine as well. What we usually use is a dilute solution of hydrochloric acid. Vinegar is simply much more readily available to most people.

If the rock is quartz, it will not have any effect on the pH. If it contains dolomite or calcite, a few days will not be enough time to see any appreciable effect on the pH unless the water it's in is acidic. Dissolution of carbonate minerals in neutral solutions takes a very, very long time.