What stats does Radiant Gargoyle Stoneplate give?

Radiant Gargoyle Stoneplate grants 300 HP and 50 Armor.

What kind of item is Radiant Gargoyle Stoneplate in TFT Set 17?

Radiant Gargoyle Stoneplate is a Radiant item in TFT Set 17.

Gain 20 Armor and 20 Magic Resist for each enemy targeting the holder.

radiant

Gain 20 Armor and 20 Magic Resist for each enemy targeting the holder.

Armor

The physical-defense stat that reduces incoming AD damage. Tank items, the Bastion trait, and champions or items that grant flat Armor all feed into this mechanic, alongside the handful of effects that scale a bonus off a unit's Armor value. Sunder is its inverse — a debuff that reduces enemy Armor.
Magic Resist

The magic-defense stat that reduces incoming AP damage. Many sustain items, the Bastion frontline trait, and "Gain X Armor and Magic Resist" effects grant or scale off it; Shred is its inverse.