Florencite-(Sm) is a very rare mineral of the plumbogummite group (alunite supergroup) with simplified formula SmAl<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>. Samarium in florencite-(Sm) is substituted by other rare earth elements, mostly neodymium. It does not form separate crystals, but is found as zones in florencite-(Ce), which is cerium-dominant member of the plumbogummite group. Florencite-(Sm) is also a samarium-analogue of florencite-(La) (lanthanum-dominant) and waylandite (bismuth-dominant), both being aluminium-rich minerals.
Florencite-(Sm) was revealed in quartz veins in the Maldynyrd Range, Subpolar Urals, Russia. It associates with xenotime-(Y).
Florencite-(Sm) has admixtures of neodymium, and small amounts of cerium, gadolinium, sulfur, strontium, praseodymium, calcium, lanthanum, europium, and silicon.