ΔE 20.7, loose: different enough that you should pick on purpose. Sparkling Amethyst is noticeably darker, much more saturated than Mithril.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Sparkling Amethyst is noticeably darker, much more saturated than Mithril.
The same difference applies the other way round: Mithril is noticeably lighter, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Mithril on the colour wheel See Sparkling Amethyst on the colour wheel
All matches: Mithril equivalents · Sparkling Amethyst equivalents