I need to make a carrier that will hold a piece 2.5"x2.5"x.5" piece of graphite.

Any suggestion on a carrier that will work good for that size?
Thinking about taking a piece of mdf and cuting a square out and using that but retaining the piece is my concern.
Hot glue or two sided tape would eventually tear the board. Not sure if i tape the edges down it would hold the graphite.

John