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Old 07-24-2019, 06:56 PM
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Default A couple of questiosn about rocks.

Okay, so I have some questions about rocks that I hope someone can answer.

1. I'm looking into buying black lava rock from an online supplier here. But I don't know how many kilos we're looking at here. I understand the density is different in lavarocks mostly but, with black icelandic lavarock, what sizes or portions can I estimate from like, maybe 2 kilos? 4 kilos? 6 kilos? I want to re-do my viv with lavarocks, and ideally I'd want atleast 2 fairly big ones (maybe 30 - 40 cm high, 15 - 20 cm wide) If I want 2 around 30 cms, what ballpark am I in, weight wise? I'm not set on lavarock in the viv, I'd like to find some rocks in my yard/locally too of course, but then comes my second question.

2. When googling rocks and fishkeeping in norwegian, I'm getting mostly "this rock cannot be used" etc, that all rocks that glimmer are bad, etc. And I live in an area where there is a lot of "bad" minerals seeping into rocks etc (does mineral seep? idk) But, like a lot of "unpure" rocks. Yet, I see all sorts of rocks in riverbeds, lakes, bodies of water etc that do no harm as far as I know.

What are your experiences with this? Have you tried using rocks that supposedly are "bad" ? What was the result?

3. So, in my area, whenever they do road work or any sort of gravel work, we end up with some rocks laying around that look like green glass/green jade. I know it's obviously not jade, but it looks very cool and has a very smooth,glassy feel. I recently found a piece I fell in love with, with some "ombre" green. I haven't found any really big pieces yet, but I'm wondering, what type of rock this is? Or if it's a rock at all and not just some by-product.

Here's an image of it

And, can it be used in fish tanks/vivs or will it leak something bad? If it's just some glass-byproduct, it's probably safe?
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Old 07-24-2019, 07:09 PM
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Default Re: A couple of questiosn about rocks.

1) Have you tried contacting the supplier? They could throw a rock on the scale and tell you exactly what you want to know.

2) Some rocks contain metals, which under certain environmental conditions can leach into water. Some of those metals are toxic to fish and aquatic invertebrates (and, possibly but not too likely, frogs). Some (many) rocks change the pH and hardness of water they contact by dissolving into that water. For some fish, this is a negative change. In local waterways, aquatic inhabitants have evolved to live in that water, but most folks keep non-native fish in aquaria.

3) I don't know what that is exactly, but it looks like some sort of stable igneous rock. I would personally use it and not worry. I'm not remotely a geologist, though. (I think Encyclia is; hopefully he'll comment here).
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Old 07-24-2019, 07:20 PM
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Default Re: A couple of questiosn about rocks.

Oh yes, I should have specified, I know some change hardiness of water etc, that's fine (Or, atleast not a mayor concern. I don't have fish in my vivs, but if I would, I would have made sure to fit the water hardiness with what fish type prefers it etc)

The supplier sold it by kilos and stated you could request sizes upon ordering. But I'd rather have an idea beforehand. Perhaps I should just e-mail them and ask for a scale or somehow a more detailed measurement, haha.

Oh man, if it's a type of rock I could use, that would be cool!

edit: so after some google-fu, I'm snooping around the stone types Tourmaline/Dravite, which occurs where I live. Hmm.

Last edited by sparrow; 07-24-2019 at 07:25 PM.
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Old 07-24-2019, 08:30 PM
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Default Re: A couple of questiosn about rocks.

That looks a lot like green obsidian, especially the way it fractured.

https://www.gemsociety.org/article/g...oxicity-table/

^I wasn't able to find very much on it, but it's supposed to have a low chance of silicosis --- if ingested.

My suspicion is that it's not going to cause a problem, but I wouldn't put it in yet.

EDIT: On estimating the weight of rocks / minerals, if you are pretty sure which kind of rock you want, you can find the density of the rock, estimate the size of the rock quantity you want, and get a rough idea of how much space a certain weight of rock will take up.

For instance, the density of granite is 2.7g/cc I believe. A 10cc * 10cc * 10cc cube of it would weight 2,700g (2.7kg). So if you ordered 30 kg of granite blocks (just as an example), you can roughly estimate that you'll get 11 cubes of 10cc^3.

If lava rock is a consistent 2g/cc (or whatever it is), 1,000cc of it is going to be 2kg. You can work backwards to get a rough idea of how big the package is going to be if it's, say, 20kg. You can never get an exact idea because you don't know how many rocks are going to be in that package, or whether or not there are inconsistencies in what they call lava rock, or how faithful the seller is to giving you an actual 20kg package. You can kind of get an idea, though.

Last edited by Kinstrome; 07-24-2019 at 08:43 PM.
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Old 07-24-2019, 08:34 PM
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Default Re: A couple of questiosn about rocks.

Greetings,

Rocks of various kinds can certainly leech minerals (rather than "seep" them) - and this can be a problem in a closed system. Rivers and oceans are more open systems were local mineral concentrations are diluted and/or carried away so they do no harm. If your setup includes a drain for waste water so that dissolved mineral concentration doesn't increase over time in the false bottom, you should be okay using most rocks.

Since lava rock can vary in density, it would be hard to estimate the amount of rock you'll get for a given weight or volume.

The green, glassy rocks you mentioned as coming from roadwork sites is likely slag - a byproduct of metal extraction from ore. Being the outcome of a high-temperature process, slag is certainly stable but I would be somewhat concerned about the unknown mineral content that could pose a leeching problem.

Update: Here's a PDF that discusses leechate from slag: http://www.nationalslag.org/sites/na...eachate_bf.pdf

It sounds like the main issue with leechate from slag is hydrogen sulfide (H2S) production - but Manganese (a toxic metal) is also present in slag so that could be a concern as well. A few pieces of the slag rock in your viv should be fine - but I would not use the slag as a major component of the substrate.

Last edited by kimcmich; 07-24-2019 at 08:42 PM.
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Old 07-24-2019, 08:37 PM
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Default Re: A couple of questiosn about rocks.

Quote:
Originally Posted by Kinstrome View Post
That looks a lot like green obsidian, especially the way it fractured.

https://www.gemsociety.org/article/g...oxicity-table/

^I wasn't able to find very much on it, but it's supposed to have a low chance of silicosis --- if ingested.

My suspicion is that it's not going to cause a problem, but I wouldn't put it in yet.
Oh yeah, good eye. It def. looks like obsidian.

Seems others have used that in tanks before with no problem with the rock itself except for sharp edges - but if I put it in a tank, it will only be in a tank with some micro rasboras or something.
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Old 07-24-2019, 08:40 PM
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Default Re: A couple of questiosn about rocks.

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Originally Posted by kimcmich View Post
Greetings,

Rocks of various kinds can certainly leech minerals (rather than "seep" them) - and this can be a problem in a closed system. Rivers and oceans are more open systems were local mineral concentrations are diluted and/or carried away so they do no harm. If your setup includes a drain for waste water so that dissolved mineral concentration doesn't increase over time in the false bottom, you should be okay using most rocks.

Since lava rock can vary in density, it would be hard to estimate the amount of rock you'll get for a given weight or volume.

The green, glassy rocks you mentioned as coming from roadwork sites is likely slag - a byproduct of metal extraction from ore. Being the outcome of a high-temperature process, slag is certainly stable but I would be somewhat concerned about the unknown mineral content that could pose a leeching problem.
Yeah, this was and is my initial theory. Slag. I've noticed that on some larger pieces, the inside is frothy like pumice almost. Not quite as frothy, but close. They also seem to have the same density/weight as clay, you know that green clay they use in road work and stuff.

I tried looking up like petrified clay or something, but to no avail.
I'm not about to chuck it in a tank just yet anyway!
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