I live in the countryside of Western Europe by the beach with a temperate climate. After a period of unusual humidity at 84%, I noted this white fluff in the basement floor:
The first picture is about 40 cm and the second 10 cm.
The basement is usually closed and keeps humidity. Temperatures average 18-20ºC, and humidity is now 77%. I assume it's a fungus since the floor was clear before and it seems to collapse when I rub my foot on it.
What is this species, and how can I prevent it?
Update: Following @anongoodnurse's suggestions, it's definitely a salt. I scraped the stuff, poured water, and it shriveled instantly. Here are photos before and after:
Here is a close-up of another piece, where the shards look like a crystal:
It did not smell indeed, and I did not taste it. I opened the basement door to ventilate the area, and I understand that it would accelerate the evaporation of the salty water.
I don't know if this growth has happened before, e.g. because of a leak in a pipe, or is a one-off occurrence, e.g. because of the unusual humidity in the last few weeks. I will check if the basement has any pipes.