This is the 12983rd most frequent Swedish word.
sällsynta
Rare.
The word 'sällsynta' here is used as an adjective modifying 'djurarter' (animal species) to describe that these species are not commonly found.
Det finns sällsynta djurarter som lever i Amazonas regnskog.
There are rare animal species living in the Amazon rainforest.
In this sentence, 'sällsynta' serves as an adjective modifying 'mineraler' (minerals) indicating that the minerals are uncommon and therefore may have a unique value.
Sällsynta mineraler kan vara värdefulla på grund av sin ovanlighet.
Rare minerals can be valuable due to their rarity.
Here, 'sällsynt' works as an adjective describing 'samling' (collection) to imply that the collection is unique and not readily available.