Algae ID on the back wall?

[Vtudor21]

I have some new algae(?) growing on the back wall of the tank. It's pretty hard to get a sample of it, as it feels like a crust, so I tried to scrape some and look under a microscope. Here are some pictures, please let me know if you have any clue on what it could be.

I'm hoping it's some type of coralline but I'm the opposite of an expert(to read: clueless beginner)

 

[Vtudor21]

A picture of it in the tank. It's the best I could do, given there's not a lot of it in there.