Board Game Arena

I'm new to the game and have tried to find out about large crystal tiles and have a few questions about them.

Do they count as crystals for the purpose of scoring or anything else eg building next to them?
If building or populating beyond them do they count as one space or multiple spaces?
Can you populate them?
Is it possible to play without them?
Presumably they always have the same back so more experienced players know which ones are large crystals?

Maybe some of these questions may be daft, but I'm curious about them and have tried to look in various rule sets to find out more about them.

Many thanks in advance.

1. Yes, they count as a crystal just like the ones on the borders
2. You can't count them, they are impassable terrain
3. No, no population on them
4. Yes, they are optional
5. Yes, they always have the same back with the 4 gears cost to explore.

What I find kind of annoying is, you can take them out but you can't take out the artifact cards that have crystal spots for points. And even with them in they are pretty bad imo, and I think select one of two, is just flipping the same card over that both have crystal spaces on them.

Imo, you're going to collect the others fairly naturally, but crystal spaces you would really need to target and then you're just getting one cr@py resource instead of machine tracks or water spots.