Wow you guys are awesome! Really!
I assumed it was diatoms, but it is only in the corners, not everywhere in the tank.
About the texture, i wiped it with a paper towel a few times and it feels slimy, but takes 2 or 3 wipes to take it all off. Maybe because its hard to reach in the corner? Im not sure whether its just me or if it really doesnt come off easily.