I can be Dutch or French, among others. Wheel or wedge, or grated for all that matters. I can have mold but don't throw me away. Not all mold is bad per se.

I can be a support, hold things together, or help open and close. I enclose words in a sentence or symbols in an equation. In March, you might join the madness and fill me out.

My first part is black and comes from the earth, but cannot be put into a Christmas Stocking - My second part can

I have leaves, but I am not a tree. I have spine, but cannot stand. I collect thoughts, but have no brain. I am often filled, but never full. What am I?

Grow in caves from the ceiling, Slow I am made by water dripping.