Calling water chemistry experts, and geologists

[mel_20_20]

I have Texas holey rock that I am planning to send out to AC members. I wish I could sandblast it, but I'm still looking for an answer locally on cost of that, however, I found that I was able to make it look prettier and smooth off some sharp edges with a piece of sandpaper.

Question #1: The sandpaper says "Aluminum Oxide" on the back of the paper. I guess this is the "grit" on the paper (who knew they don't use sand on sandpaper anymore,lol).

If I use the sandpaper will the aluminum harm the rock, will it cause the rock to hold onto the "aluminum" somehow and cause problems for aquatic life.

The one piece of rock I worked on was really improved with the sandpaper. Took off the sharp edges that I was worried might cause a problem for fish or snails.

Question#2: Some of the holy rock has other, what appears to be something else and not limestone. I was even able to break some of that type of rock off the limestone portions.

These rock portions are very gritty, granular, reddish as if it has iron oxide in it. Really, looking at some of it, one might think it was just dried red clumps of hard clay/soil that had become stone; it doesn't wash off or rub off like it would if that were so.

A few other pieces of the rock that I dug up look unusual. Hard fine surfaced, almost marble-like, maybe a basalt surface with holes in it that reveal the interior is like a red sandstone that has tunnels in it like the white holey rock does. An example of this rock just described is in my thread with pics:

http://www.aquariacentral.com/forums/showthread.php?t=187349

It is the rock in the 4th picture in the above thread.

The same rock is labled #8 on this page at this thread:

http://www.aquariacentral.com/forums/showthread.php?t=187349&page=4

Question #3: Does anyone know what that rock is? It is very pretty, but I'm wondering if that red does indicate Iron content, then would that be harmful in a tank?

[leeser28]

Hey Melody - you know me I see chemistry and can't wait to join, but sadly I don't have any answers. But you know I'll be following this thread (and your rocks are fantastic by the way - I've been sick and don't think I replied to your thread, but they're great!!)

[petluvr]

Looks to me to be some type of mudstone more specifically claystone. Is it soft?

[mel_20_20]

It's hard, but not terribly hard, and it breaks off if I hit it hard and chip away at it. It does look a lot like mud that has lithified. Maybe that's all it is.

It has left a fine coat of red - looks like sand - on some of the rocks, but when you wipe across it with your hand it doesn' wipe off and feels really rough. I think it could be sanded off or sandblasted off really easily.

[petluvr]

My guess would be claystone. When it breaks does it break it like sheets or just chips?

[jackiomy]

It's hard, but not terribly hard, and it breaks off if I hit it hard and chip away at it. It does look a lot like mud that has lithified. Maybe that's all it is.

It has left a fine coat of red - looks like sand - on some of the rocks, but when you wipe across it with your hand it doesn' wipe off and feels really rough. I think it could be sanded off or sandblasted off really easily.


Very cool word! Thanks.

[leeser28]

Could it be something like the red rocks in AZ?

[mel_20_20]

It does come off (when I hit it with another piece of rock or something hard) the holey rock in slab-like pieces.

Yes, Lisa, it does look like the red sandstone of the southwest, but not as hard, that stuff is pretty hard. This breaks up easier. I think the mudstone suggestion sounds right, and it would make sense.

Since limestone is a sedimentary rock, formed under pressure, composed mainly of calcium that was deposited by the remains of marine animals, corals, etc., then it would be logical that mud and sediment would undergo the same lithification process that turns the calcified skeletal remains into stone.

I think either sandbasting or even sanding with a coarse grit paper could take the residue of that stuff off the limestone holey rock.

If the red stuff is some kind of mud-rock then the red coloration probably has nothing to do with the mineral iron, and, therefore,
any remnants of it clinging to the holey rock would not cause any problems in the tank related to too much iron in the water.

I think maybe rock # 8 is limestone and dolomite. The exterior surface is so smooth, almost like polished marble, yet the inside cavernous area is that red gritty stuff. I wish I could get that one sandblasted. I bet the inside is more limestone with a coating of that mudrock residue, and would be white if I could blast that off of it.

[petluvr]

I still think claystone which is a type of mudstone. The red I am sure is from clay particles that were trapped inside the holes and did not undergo the same pressure as the rest of the rock when it was forming therefore leaving the red color.

[Cory Keeper]

On the sandpaper, I've used aluminum oxide sandpaper for years without any ill side effects. They switched to the aluminum oxide because its probably cheaper and lasts longer than your conventional sandpaper. Plus its great when working with metal too.... sand doesn't have that benefit.

[mel_20_20]

Thanks Cory... that allays my fears in that regard.
Petluvr... I think you are right that it is mudstone, and I believe that a good workover with sandpaper would get that residue off.

I wish to goodness I had a sandblaster, however, I did talk to a man that has a "media blasting" busines... He was leaving town as I walked up to his place of business and we chatted for a few minutes.

He said it sounded like I needed to have him use his blasting chamber, that uses glass beads and not sand. He said he didn't have a clue how much it would cost me because his usual charge for that machine is $75 an hour.

He said that when he gets back in town he will get me to come over with a rock and he'd play with it a little to see how much time it takes to polish holey rock.

Since I used some sandpaper on one of the rocks and saw how easily the rough edges smooth down in seconds, I think it wouldn't take long for each rock. I bet I could get 30 rocks done in an hour, depending on the weight of it and how hard it is for him to move it around inside the chamber (does it by hand with these heavy duty rubber gloves on)

Anyway, we'll see.