Stillwellite-(Ce)

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Stillwellite-(Ce)
Stillwellite-(Ce)-33971.jpg
1.3 cm stillwellite-(Ce) crystal in matrix
General
CategorySilicate mineral
Formula
(repeating unit)
(Ce,La,Ca)BSiO5
IMA symbol Swl [1]
Strunz classification 9.AJ.25
Dana classification 54.02.03.02
Crystal system Trigonal
Crystal class Pyramidal (3)
H-M symbol: (3)
Space group P31
Identification
ColorRed-brown to pale pink
Crystal habit Flat rhombohedral crystals, massive
Twinning Observed on {100}
Cleavage Imperfect
Fracture Conchoidal
Mohs scale hardness6.5
Luster Resinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 4.57–4.6
Optical propertiesUniaxial (+)
Refractive index nω = 1.765, nε = 1.780
Birefringence δ = 0.015
Other characteristics Radioactive.svg Radioactive
References [2] [3] [4]

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

Contents

Location

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

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

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

SiO2

22.4022.06La2O327.9519.12
UO20.22Ce2O333.1530.82
ThO25.41Pr2O31.82
B2O312.23[13.46]Nd2O35.36
Al2O30.42Sm2O30.34
Y2O30.740.28Fe2O30.18

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9
(Mg,Fe3+
)(SiO
4
)
6
(SiO
3
OH)(OH)
3
. The cerium and lanthanum content varies with the Ce rich species and the La rich species. Analysis of a sample from the Mountain Pass carbonatite gave 35.05% Ce
2
O
3
and 30.04% La
2
O
3
.

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References

  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. 1 2 3 4 http://rruff.geo.arizona.edu/doclib/hom/stillwellitece.pdf Handbook of Mineralogy
  3. 1 2 http://webmineral.com/data/Stillwellite-(Ce).shtml Webmineral data
  4. 1 2 http://www.mindat.org/min-3788.html Mindat.org