Will a part sand,part fluorite substrate work?

[justintoxicated]

that looks like regular flourite to me :huh:

I saw an article where they put sand and flourite together and they said it worked really well.

 

[new2tanks]

the website lists red and black as types of fluorite....

 

[Blinky]

I believe Flourite comes in solid red and red mixed with black. I've never seen any other colour, but if it's out there it would look fantastic (I love the look of plants on black gravel/backgrounds).
We have tanks at work with sectioned-off areas of different substrate. You could use cyanoacrylate glue or silicone to fix a divider (glass, slate, plexiglass) in place, hopefully that would reduce the possibility of the two mixing.