My basement is quite dry (knock on wood!). Recently I brought into the basement for the winter a table from outside. The table had some ice stuck to it which I couldn't remove, so I simply let it melt on the floor of the basement. After the puddle that formed evaporated, an interesting artifact was left behind along the the perimeter of the puddle. It's a raised white line of fuzzy material.

Here's the puddle's perimeter The puddle and it's perimeter

And here's a close-up of the line that's left behind with a clothespin for scale A close-up of the line left behind, with clothespin for scale

Is this efflorescence? I did some googling, and this is what seems most likely, but I don't know much about chemistry and thought I would ask those who would actually know. Is it something else?


  • $\begingroup$ @theo well, that may be a bit extreme. Anyway, it's something that is probably crystalline and highly soluble in water. NaCl is my best guess. Another way would be to put it on a blue flame and see if it burns yellow-orange. $\endgroup$
    – Gimelist
    Dec 20, 2014 at 19:47
  • $\begingroup$ I will happily go put some on my stove's burner and report its burning color. Sounds like more fun than tasting it. :) I'll let you know about vinegar too. $\endgroup$ Dec 20, 2014 at 20:17
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    $\begingroup$ @Michael When I poured a little vinegar on it, it fizzed and disappeared. Calcite, perhaps? Pouring vinegar on an area of the basement floor without the substance did not cause fizzing. Nor did pouring vinegar on a small platter of table salt. $\endgroup$ Dec 20, 2014 at 20:47
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    $\begingroup$ @Michael I need to revise my earlier comment: I tested it again in a flame. This time with a knife that originally did not change the color of the flame, and it clearly did when I added the white substance to it. I think perhaps the first time I tried with a "plain knife" I had not adequately washed off the substance. $\endgroup$ Dec 20, 2014 at 20:55
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    $\begingroup$ also, being a bit reckless, I tasted it. It's salty, but not quite like table salt. Almost a stingingly-sharp saltiness. $\endgroup$ Dec 20, 2014 at 20:58

1 Answer 1


Three pieces of information from the comments:

  1. It fizzed and disappeared in vinegar.
  2. It had a yellow-orange color in blue flame.
  3. It's salty (note that it's usually a bad idea to taste random stuff you find on your floor).

The only white crystalline material that is a plausible candidate for being there and fizzes in acetic acid (ie vinegar) is calcite - $\ce{CaCO3}$. It's also a mineral that has 'retrograde solubility' meaning it dissolves more readily in cold water. This is probably how it got to the water in the first place. This is also why it precipitates on your electric kettle. It is the same stuff.

The salty stuff that burns yellow-orange is obviously $\ce{NaCl}$, aka table salt. It also probably dissolved with the vinegar as well. Why is the salty taste not quite like table salt? Well, first of all it is mixed with calcite. But, calcite has no taste. It's possible that there is some $\ce{KCl}$ or $\ce{MgCl2}$ in there as well. They are slightly more bitter than $\ce{NaCl}$. This is the stuff they use in low sodium salt.

There's another possibility - it could be any of the epsom salt family, $\ce{MgSO4.$n$\,H2O}$.

As to would this be dissolved in the first place, you can only speculate. You say that it came from a table that was outside. Did people eat there? Could people had spilled salt on it? Is the airborne dust in your area contain a lot of calcite? What about your basement? Could someone have spilled some salts on the floor, maybe even years ago?

  • $\begingroup$ so am i correct in understanding your answer to say that the substance is a mix of both CaCO3 and NaCl? would make sense to me... $\endgroup$ Dec 20, 2014 at 22:13
  • $\begingroup$ Most likely, yes. $\endgroup$
    – Gimelist
    Dec 20, 2014 at 22:14
  • $\begingroup$ Thanks - it's all just out of curiosity, not of any real need to know. is it the evaporation that pulls the minerals from the floor? or are they more likely already present in the water? $\endgroup$ Dec 20, 2014 at 22:18

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