Melanoma is verrrrry slow to spread. The lesion must be biopsied to know for sure. If it's melanoma and caught early enough, it's 100% curable with excision of the lesion with appropriate border tissue taken. (I know; I am a melanoma survivor!).
Just because it's black, though, doesn't mean it's melanoma. You can't look at it and know for sure. Could be a lot of other things.
Let us know how it turns out. Hugs to you!