sal ammoniac, sand, pebble
磠 centers on granular mineral substances: sand, pebbles, and the mineral sal ammoniac. The meanings are connected by the idea of small, loose, earthy or crystalline particles.
磠 combines 石 (stone) with 鹵, which likely contributes the sound and relates to salt or mineral substances. The exact historical development is uncertain.
The left side is a stone 石, and the right side 鹵 looks like a container for salt or minerals. Picture a stone container filled with sand, pebbles, and crystalline sal ammoniac.
For ロ, imagine a row of pebbles and sand lined up on a stone: row -> ロ, and the stone holds the granular minerals.