Q. I have mint oil, made by extracting it from the mint leaves. What Brachah, if any, is said upon smelling the oil? If I boil the leaves, do I still make a Brachah on the smell?

A. On the essential oil of aparsemon (known also as balsam or possibly commiphora opobalsamum) our sages instituted the special blessing of “Creator of pleasant oil” (Brochos 43a, Shulchan Aruch O.H. 216: 4). Poskim debate whether that blessing is said on other oils that are not exclusively grown on Eretz Yisroel (Talmidey Rabenu Yonah on Brochos 31b). Shulchan Aruch (ibid. 5) writes that on aromatic olive oil you recite; “Who created trees of fragrance” when it was extracted by expression. Mishna Berurah (ibid. 25) rules that this brocho applies only on essential oils of fruits; otherwise the blessing is “Bore Miney Bessamim”.

See previous answer in regards to essential oil that was extracted by distillation.
If the purpose of the mint oil was for use in a tea or beverage infusion, many Poskim maintain that you don’t recite a brocho at all (See Piskey Teshuvos 226: 7 for sources) in regards to coffee and fresh bread aroma.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a