Brick mould/fungus issue

[flakeybricks]

Hi, I've got a fireplace that looks to have poor ventilation, and no fire in it.

I've recently noticed there is a white mould growing on the concrete floor.

Does anyone know what it could be and whether it is ok to wipe up, or whether there is some other issue that could be causing it.

Thanks, Adam 

[Mike]

It looks like efflorescence to me - crystalline salt deposits. Crush some and it should turn to powder. It's caused by the presence of moisture though, so eliminating that would be the long-term solution (as it would be for mould too).