Florencite-(Sm)

Florencite-(Sm) is a very rare mineral of the plumbogummite group (alunite supergroup) with simplified formula SmAl₃(PO₄)₂(OH)₆.^[4] 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),^[2] which is cerium-dominant member of the plumbogummite group.^[5] Florencite-(Sm) is also a samarium-analogue of florencite-(La) (lanthanum-dominant) and waylandite (bismuth-dominant), both being aluminium-rich minerals.^[4]

Florencite-(Sm)
General
Category	Phosphate mineral
Formula	SmAl3(PO4)2(OH)6
IMA symbol	Flo-Sm[1]
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral (3m) H-M symbol: (3 2/m)
Space group	R3m
Unit cell	a = 6.972, c = 16.182 [Å]; Z = 3
Identification
Color	Colorless, pale pink, pale yellow
Crystal habit	Sub-mm zones in florencite-(Ce) crystals
Cleavage	{0001}, distinct
Fracture	Uneven
Mohs scale hardness	5.5-6
Luster	Vitreous to greasy
Streak	White
Density	3.6 (measured)
Optical properties	Uniaxal(+)
Refractive index	nω=1.70, nε=1.71
References	[2][3][4]

Occurrence and association

Florencite-(Sm) was revealed in quartz veins in the Maldynyrd Range, Subpolar Urals, Russia. It associates with xenotime-(Y).^[2]

Notes on chemistry

Florencite-(Sm) has admixtures of neodymium, and small amounts of cerium, gadolinium, sulfur, strontium, praseodymium, calcium, lanthanum, europium, and silicon.^[2]