na-adjective
Describes something that occurs infrequently or is hard to find. Often used as a na-adjective or adverbially with に.
この地域では雪はまれです。
Snow is rare in this region.
彼はまれにしか遅刻しない。
He is seldom late.
珍しい is an i-adjective meaning 'unusual' or 'rare' in the sense of being surprising or noteworthy. まれ is a na-adjective that emphasizes low frequency or scarcity.
The exact derivation is uncertain. The kanji 稀 and 希 both carry meanings of 'rare' or 'sparse' and are used interchangeably for this word.