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Does anyone know what these white crystals are?

As you an see they are growing out of some floor tiling in my house. They have been appearing for some years now out of the floor, which is cleaned fairly regularly (at least, I assume so, since my cleaner does it!). They may appear more frequently when the weather is humid.

For scale, the tile is 20cm each side. The crystals form light fluffy heaps, rather like snow and would be a few millimeters in height.

My guess is that they could be common salt, or possibly something connected with the bleach or cleaning products used on the floor. The latter case prevents me from trying the taste test to prove the former.

White crystals

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  • $\begingroup$ To me, this looks more like the salts washed out from concrete (or brickwork, or whatever is beneath those tiles), akin to the thing known as "wall saltpetre". $\endgroup$ – Ivan Neretin Jun 7 '16 at 18:25
  • $\begingroup$ Does is give bubbles with vinegar? en.wikipedia.org/wiki/Efflorescence $\endgroup$ – aventurin Jun 7 '16 at 18:44
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    $\begingroup$ No bubbles in vinegar. $\endgroup$ – rghome Jun 7 '16 at 19:41
  • $\begingroup$ Having Googled it, it seems probably it would be wall saltpetre. I had a soil pipe break under the house a few years back and the ground would likely have become saturated with a good source of water, potassium and nitrogen, not to mention the ammonia in cleaning agents. I guess the tiles must be porous, especially where the surface is damaged, as in the picture. $\endgroup$ – rghome Jun 7 '16 at 19:50

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