Melted Rock Mystery

[Lifeisgood]

Can anyone help me to identify a mineral/rock which melted in my aquarium?

It was a fist sized white rock with grey veins in it.  Thought it was quartzite.  Vinegar does not make it fizz. It melted down to a few thin chips (pictured below). It only took three months for this to happen.

It made the water smell like sulfur and caused a white growth on the substrate that was soft and floated easily when disturbed. (Pictured below).   I thought it was a fungus and had to aggressively siphon it and affected substrate out to get rid of it.

It did not kill any fish but did affect water quality—because the fish were less active and worked their gills more rapidly.

It did kill plants by destroying their roots.

Any ideas what the mineral or rock was?  Any suggestions as to how I can test remaining chips?  I have to admit that I licked it to see if I could taste salt 😝(but it doesn’t have a taste).

Just wanting to learn.

[PineSong]

Super interesting and I have no idea but will eagerly wait to hear what others say. You get bonus points for licking it! Science mind at work, for real!

[Odd Duck]

I suspect your rock may have been white calcite.  Did your pH or GH change?  I would expect both to increase if it was calcite. 

[Lifeisgood]

On 12/29/2021 at 1:36 AM, Odd Duck said:

I suspect your rock may have been white calcite.  Did your pH or GH change?  I would expect both to increase if it was calcite. 

I have very hard water.  GH shows more purple than the darkest purple on the AC test strips.  I don’t remember what the readings were before adding the rock.  But comparing it with another established tank I have with plants, the same driftwood—and water:

ph was low in both but was .4 higher in the tank with the white stone.

kh was 40 in other tank but 80 in the one with the stone.

Could calcite have sulfur in it?

[Odd Duck]

It doesn’t typically have sulfur in it, but could potentially be contaminated by sulfur.  The sulfur smell is more likely to be a disturbed gas pocket.  How certain are you that the rock dissolving caused the sulfur smell?

[Lifeisgood]

On 12/29/2021 at 3:51 PM, Odd Duck said:

It doesn’t typically have sulfur in it, but could potentially be contaminated by sulfur.  The sulfur smell is more likely to be a disturbed gas pocket.  How certain are you that the rock dissolving caused the sulfur smell?

I wasn’t aware that the rock was melting and thought I was dealing with a white fungus issue.  As the white growth spread the smell of sulfur increased.  I would siphon it out the smell went away.  The white growth kept returning even after treating a full round of Pimafix.  Since I got all the shards of white rock out, no more white growth and no more sulfur smell.🤷‍♀️

[Odd Duck]

Very interesting!  I’m not sure what was happening, but it sure would be interesting to know.  I don’t suppose you have any of that rock left?

[Lifeisgood]

On 12/31/2021 at 11:47 AM, Odd Duck said:

Very interesting!  I’m not sure what was happening, but it sure would be interesting to know.  I don’t suppose you have any of that rock left?

Yes, I still have the shards that are in my hand in the picture.  Do you have suggestions as to how to test it?

[Odd Duck]

On 12/31/2021 at 11:14 AM, Lifeisgood said:

Yes, I still have the shards that are in my hand in the picture.  Do you have suggestions as to how to test it?

Does the rock smell of sulfur when dry or wet?  If it doesn’t smell of sulfur either way it’s not likely the source of the sulfur smell.  Could be the speed of the melting was driven by pH changes that happened in the water due to H2S release from the substrate?  Purely speculating here.  If the rock smells of sulfur, then I’d say it was the rock.

Even though I’ve had far too much chemistry for my degree, I’m not a chemist at all.  My chemistry classes were all as background for medicine.  I can usually follow along, but I’m not one that can tell you off the top of my head how to run a test on something like that.

Let me see if Google can help us.

[Odd Duck]

Some quick reading indicates testing for sulfur can be challenging and involves some pretty toxic chemicals and fancy, expensive equipment.  Also that it can be hidden in rock seams as pyrite which can be dark and even look black or grey.  Elemental sulfur is yellow, but compounds can be other colors.

It seems like there could have been some pyrite and therefore sulfur in the greyish seams in your rock?  I would guess that your rock samples could potentially be sent in to a soil analysis place?  If you’re interested in testing, I would start with a phone call to a local soil testing lab and see if they can do the testing.

[dasaltemelosguy]

Just a 2c but if you placed one in 5ml of water and let it sit overnight or even heat it, then run typical water tests. It may provide some info on what it does when it dissolves as it would be very concentrated. Those cheap 15-test water test strips might even detect whatever it is if you can concentrate the leaching to 5ml or so. Intriguing find you have there!

[Fonske]

On 12/29/2021 at 4:46 AM, Lifeisgood said:

Can anyone help me to identify a mineral/rock which melted in my aquarium?

I can't identify it, but I have a story to tell about a rock that looked very much like yours. So in a local park near me there are many signs/panels that I thought were made of white marble or granite -- white, sparkly mineral with gray veins. The last summer several of these panels broke into pieces. They were just laying around for several weeks and eventually I decided to pick some up and maybe use them in my tanks. But the mineral/material crumbled in my hands like moist sugar.

My guess is that 1) it was an artificial marble imitation material; 2) it was made of marble particles held together by a glue or cement and 3) the last summer was unusually rainy and the water destroyed the "glue".  

[Hobbit]

OHHHH could it be gypsum??

Gypsum is fairly soluble in water and contains sulfur!!!!!!

https://en.wikipedia.org/wiki/Gypsum

It can come in a pretty crystal form but also a white powdery form with veins.

[Fonske]

On 12/29/2021 at 4:46 AM, Lifeisgood said:

Any suggestions as to how I can test remaining chips?

If you can make a scratch on it with your fingernail, it's very likely gypsum.

[Lifeisgood]

On 1/1/2022 at 11:06 AM, Hobbit said:

OHHHH could it be gypsum??

Gypsum is fairly soluble in water and contains sulfur!!!!!!

https://en.wikipedia.org/wiki/Gypsum

It can come in a pretty crystal form but also a white powdery form with veins.

I think this makes perfect sense!  We have a gypsum mine nearby and samples from it can appear in unsuspecting places.. I got this rock out of one of the many boxes in our garage—our family likes to collect rocks from everywhere we go.

Something about my water made quick work of dissolving that gypsum for sure!  Thanks to everyone for helping me figure this out!  😁

I love being part of this community!

[Lifeisgood]

On 1/1/2022 at 11:25 AM, Fonske said:

If you can make a scratch on it with your fingernail, it's very likely gypsum.

I thank you for suggesting the “scratch test”.  I can scratch it!  Mystery solved!!

So we can add gypsum to the list of rocks not to add to our aquariums—and now we know what it will do and can ask a person about their rocks if they are struggling with a white “fungus” growth on their substrate!🤯😊