It all depends on where you are ?
Some STATES, Ariz/NM, etc, if you are a resident,
Will perform a certain number (3-4?) of assays for FREE!
OR!
Can have them done at a private assay office
&
Depending on what kind of assay you have done
Either For & Only, a "specific" mineral
ie: Gold or silver or etc
The cost runs around $20 or so !
Per mineral
OR!
Even BETTER
You could get a "Spectrographic" Assay (the Best kind) done
It will "ID" any, 80-90, different kinds of minerals