Most often appears in the comparison phrases 坚如磐石 (solid as a rock) and 稳如磐石 (steady as a rock) - used for friendships, alliances, foundations, resolve. Almost never used to literally describe a rock today.
memory
磐 shows 般 (sort/kind) over 石 (stone) - "the kind of stone" that is huge and immovable. The 石 below also doubles down on the second character of the word.
