I want to create a world for my colonists that's bleak and unwelcoming as well as alien and strange.
So to that end I wanted to make mushroom-like fungi the major flora on the planet. I've read Where do mushroom forests thrive? for some inspiration. I don't need forest-sized growths, but to make it more alien I thought having a calcium carbonate structure would give a ghostly white appearance, similar to deep-sea coral that have made this trade-off compared to soft coral that uses chitin.
But what would give rise to this? What is gained for swapping chitin for calcium carbonate?
The only thing I can think of is that it would be necessary if there were extreme winds, but even then I'm not sure.