Stillwellite-(Ce) is a rare-earth boro-silicate mineral with chemical formula (Ce,La,Ca)BSiO5.

Stillwellite-(Ce)
1.3 cm stillwellite-(Ce) crystal in matrix
General
CategorySilicate mineral
Formula
(repeating unit)
(Ce,La,Ca)BSiO5
IMA symbolSwl[1]
Strunz classification9.AJ.25
Dana classification54.02.03.02
Crystal systemTrigonal
Crystal classPyramidal (3)
H-M symbol: (3)
Space groupP31
Identification
ColorRed-brown to pale pink
Crystal habitFlat rhombohedral crystals, massive
TwinningObserved on {100}
CleavageImperfect
FractureConchoidal
Mohs scale hardness6.5
LusterResinous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity4.57–4.6
Optical propertiesUniaxial (+)
Refractive indexnω = 1.765, nε = 1.780
Birefringenceδ = 0.015
Other characteristics Radioactive
References[2][3][4]

Location

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It occurs as a metasomatic replacement of metamorphosed limestones in the Mary Kathleen mine, Australia and in alkalic pegmatites associated with syenite in an alkaline massif in Tajikistan.[2] It occurs in association with allanite, garnet, uraninite in the Australian deposit; with calcite, monazite, bastnasite, thorite, uranothorite and thorianite in the Desmont mine, Wilberforce, Ontario, Canada; and with pyrochlore, tienshanite, sogdianite, thorite, caesium kupletskite, reedmergnerite, steacyite, pectolite and quartz in the Tajikistan deposit.[2] It has also been reported from Mont Saint-Hilaire, Quebec, Canada and from Mineville, Essex County, New York. Other occurrences include the Inagli massif, Yakutia, Russia, around Langesundsfjord, Norway, in the Ilimaussaq intrusive complex, southern Greenland and the Vico volcano, Lazio, Italy.[2]

Discovery

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It was first described in 1955 for an occurrence at the type locality is the Mary Kathleen mine, 55 km (34 mi) east of Mount Isa, Queensland, Australia. It was named for Australian mineralogist Frank Leslie Stillwell (1888–1963).[3][4]

Chemistry Breakdown

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(1) (2) (1) (2)

SiO2

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22.40 22.06 La2O3 27.95 19.12
UO2 0.22 Ce2O3 33.15 30.82
ThO2 5.41 Pr2O3 1.82
B2O3 12.23 [13.46] Nd2O3 5.36
Al2O3 0.42 Sm2O3 0.34
Y2O3 0.74 0.28 Fe2O3 0.18

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d http://rruff.geo.arizona.edu/doclib/hom/stillwellitece.pdf Handbook of Mineralogy
  3. ^ a b http://webmineral.com/data/Stillwellite-(Ce).shtml Webmineral data
  4. ^ a b http://www.mindat.org/min-3788.html Mindat.org