宝石の国 1 [Hōseki No Kuni 1] by Saou Ichikawa

In a world inhabited by sentient gemstones, each representing a different mineral, the story follows Phos, a young and fragile gem who struggles to find their purpose among their more battle-hardened peers. Tasked with compiling an encyclopedia, Phos embarks on a journey of self-discovery, navigating the challenges of their unique society while facing threats from the mysterious Lunarians, who seek to capture the gems for their own purposes. Through encounters with fellow gems and the enigmatic Cinnabar, Phos learns about the complexities of identity, duty, and the desire for transformation.