I'm trying to get what you're saying. "Useless form," does that apply to coal or a diamond (I assume you reference diamonds and coal in this poem). Because both are actually useful. I think coal is the useful form is this poem, just the 'not beautiful' form. Are you saying that since a diamond has less use than coal, making a diamond (which is beautiful) has the sacrifice of not having some coal?

Hmmm, qutie possible. My own interpretation is that under the coal's ugly appearence, there's beauty underneath it. And i think he's saying that all coals are potential diamonds but to get to that diamond, one has to work hard to get/see it.

Aken Sol

BTW, done with both responses