Almost never stands alone. You'll meet it in 硫磺 (sulfur), 磺胺 (sulfonamide), and the technical 磺酸 (sulfonic acid). The 石 radical signals a mineral / inorganic substance.
Stone radical on the left marks 磺 as a mineral - sulfur was historically mined as yellow rock from volcanic deposits. Same radical drives 矿 (ore), 砂 (sand), 碳 (carbon), 硫 (sulfur - pairs with 磺 in 硫磺). Stone radical is the standard for elemental and mineral chars.
黄 supplies the sound directly - huáng with matching tone - and adds strong semantic reinforcement: sulfur is the bright yellow mineral. This is one of the cleanest phono-semantic pairs in chemistry vocabulary, both halves transparently doing their job.
