Anime/cartoon about various gems giving powers to their holder

There's a remote chance you're thinking of the cartoon adaptation of The 99.

To summarize, the "power" of the books of Baghdad's House of Wisdom was absorbed into 99 gems before the library was destroyed by invaders. These stones are slowly being recovered, and imbue their owners with various super powers.

The show had a brief run in the US in 2011.

I think you are looking for Power Stone. You can see the intro below:

The guy with red armor is Falcon

Falcon's Power Change is a red android-like form able to launch many missiles. He is also able to fly with the rocket on his back, but in the games, he only does so when using Power Rocket. In the anime finale, Falcon's second Power Change form, using the Light Stone, is a white jet-like android with black and yellow eyes and angelic wings.

The guy in samurai armor would be Ryoma.

Ryoma's Power Change is a beetle-like silver samurai with electric powers.

The girl with fire powers is Rouge:

Though her normal attack and defense abilities are relatively low, Rouge can wield her fire attacks from a long distance and inflict severe damage. Her running and jumping speeds are also higher than the other fighters.

During Power Change, she has a genie-like appearance with fiery hair. A fireball with an eye follows her. In the anime, she can summon a magic carpet that can fly after she rescues an injured Ryoma from a burning palace, absorbing the flames in the burning shipwreck and can melt the ice when she was in her flaming appearance.

What you are thinking about is a show called Gaist Crusher. These crystal formations would become giant monsters and when killed and stabilized, certain people could equip and use them as armor or use Form 2 which is a giant weapon and no armor but you could train and get Form 3 which was the original Gaist's form