Identity of rocks

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sdb

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May 4, 2004
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British Columbia, Canada
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I've got some rocks from my yard that I'd like to use in my tank. The LFS is way way too expensive. The problem is, I have no idea on what kind of rocks they are. I'm useless at googling, too, so I came up empty there.

The rocks are readily available in my area (British Columbia mainland, just north of Vancouver). People use them to make garden borders, rock gardens, etc. They are pretty much white with black/grey speckled all through so there is an equal amount of white and black speckled coloring. They are broken pieces, so they must come from larger rocks originally, though I've only seen them in pieces. When turned in the light, both the black and the white parts glitter a little. They aren't fancy by any means, just plain rocks from around the area, but that's why I would like to use them, they look natural.

I soaked them for 36+ hrs in a bleach solution, scrubbed them, and boiled them. They also passed the vinegar test. Do you think it's safe to use them?
 
BC is primarily a volcanic zone, and the predominant rocks are basalt and granite. both igneous, both ok in the aquarium. the rock you describe sounds like quartsite laced basalt, with a very high silica content (shiny stuff) most likely they will be perfect. there is one thing to watch for and that would be heavy metals. West coast Basalt seams often have precious metals, and heavy metals in them, so if anything looks metallic, or if you start seeing snails die off I'd chuck the rocks. It is really rare to have metals that aren't visible, so inspection should be enough to be safe in most cases.
Dave
 
Hey gonefishin, the color is quite similar, but I don't think this stuff is strong enough to be granite. If I drop it, bits break off. But then maybe granite does, too, until it has a protective coating.

I've written down what you've mentioned, daveedka, and I'm going to google the names and see if I come up with something. How would I know by looking if the rock has metal in it?
Most of the rock looks pure without any marbling, but a couple pieces are slightly discolored (redish stain) on one side, and one has a marbled section, but the marbled part is solid grey, like slate or something. (Guessing by color, not knowledge!)
 
It sounds like dave knows a bit more than I about the subject(you will soon know all I know about it, read on). I can say that raw granite is brittle. I'm not sure what makes it strong when used in things such as counter tops, but we have it all over the basin and you can crumble it like a stale doughnut in your hands.
 
I can sort of explain from a structual point of view. On the average granite countertop, forces are rarely high impact point loads (ie something pointy hitting the surface hard and fast). Granite is very strong against certain types of loads, compression especially. Shearing - no. ARgh, I need to draw pictures lol.

Anyway dropping a rock from chest height so it lands on an edge will create a large point load or a shear force (sorry about the terminology, its been awhile) will cause it to break. But if you were to stand on it, it wouldn't break. If I remember right, granite should be similar to concrete in how it reacts to different forces. On a concrete road, 1000s of heavy vehicles go over it every day, but take a pickaxe to it, and it crumbles.

Last analogy I think of is a woman in stiletto heels. If you get stepped on by one of those, you might need a hospital, but if you get stepped on barefoot, you'll just say a couple choice words.

Anyway, sorry for the confusing post -- I can visualize what I'm thinking of but I can't quite say it...
 
Well, it's definately granite. :)
Amazing how easy it is to find something when you have a name to punch into google! I couldn't find pictures of canadian granite, but it's almost identical to other granites, including the redish/pinkish color tones that are mixed in. I saw some pictures of granite countertops, too, and I can see it's the same.
I had also found some black rock with grey marble coloring in it, and by googling 'basalt', I now know that that's what it is.

Thanks, everyone, for the quick and accurate responses! I really appreciate the wonderful help.
 
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