Gemstone Array One key aspect of Gemstone Array is that it has no restriction on activations per turn or by tapping, so it is a clean way for infinite colorless mana to become colored mana
Another contributing factor to rarity is the popularity of the Pokmon featured on the card
Itzquinth, Firstborn of Gishath, Thrashing Brontodon, Wayta, Trainer Prodigy, Bronzebeak Foragers, Wrathful Raptors, Apex Altisaur, Zacama, Primal Calamity, Path to Exile, Generous Gift, Savage Stomp 10 targeted removal
10 Young Wolf Youth is wasted on the young
Note that if mana is really not a problem, they can always Past in Flames back the Gifts Ungiven they just resolved, so any card denial you manage is only a temporary measure