Fluocerite

(repeating unit)(La,Ce)F3Strunz classification03.AC.15 (03)Dana classification09.03.04.02 (09)Crystal systemTrigonalCrystal classHexagonal scalenohedralSpace groupP3c1 (No. 165)Unit cell328.80 ų (Calculated from Unit Cell)IdentificationFormula mass196.02ColourGreenish-yellowCrystal habitPlaty, tabularCleavageIndistinct, ImperfectMohs scale hardness4-5LusterVitreousStreakWhiteDiaphaneityTransparent to translucentDensity5.93Birefringence0.006

Fluocerite-(Ce)
General
Category	Mineral
Formula (repeating unit)	(La,Ce)F3
Strunz classification	3/A.10-20
Dana classification	9.3.4.1
Crystal system	Trigonal
Crystal class	Hexagonal Scalenohedral
Unit cell	320.86 ų (Calculated from Unit Cell)
Identification
Formula mass	196.99
Colour	Light yellow; darkening to yellow- and red-brown; colourless to pale pink (transmitted light)
Crystal habit	Massive, Primsatic
Cleavage	Distinct/Good
Fracture	Irregular/Uneven, Splintery, Sub-Conchoidal
Tenacity	Brittle
Mohs scale hardness	4.5-5
Luster	Vitreous, Resinous, Pearly
Streak	Yellow-white
Diaphaneity	Transparent to translucent
Specific gravity	5.93 - 6.14
Density	5.93 - 6.14 g/cm3 (Measured)
Birefringence	0.005 - 0.007

Fluocerite, also known as tysonite, is a mineral consisting of cerium and lanthanum fluorides, with the chemical formula (Ce,La)F₃.^[1][2] The end members are classified as two different mineral types depending on the cation, fluocerite-(Ce) and fluocerite-(La), corresponding respectively to lanthanum trifluoride and cerium trifluoride. Both crystallize in the trigonal system.^[3]

Fluocerite-(Ce) was first described (without the Ce) in 1845 from hydrothermal veins in granite in Sweden.^[4] Fluocerite-(La) was first described in 1969 from the type locality in central Kazakhstan.^[3] The name tysonite was given in 1880 to the same type of mineral found in Colorado.^[5][6] Tysonite-type structure is used for rare-earth fluorides with the P3c1 space group structure.^[7]

References