Dollaseite-(Ce)

Dollaseite-(Ce)
General
Category	Silicate mineral
Chemical formula	CaCeMg2AlSi3O11F(OH)
Identification
Molar mass	551.04
Color	Brown
Crystal habit	Massive, somewhat prismatic, equant when subhedral
Crystal system	Monoclinic - Prismatic
Twinning	On [100]
Cleavage	Indistinct, epidote has one good cleavage on one side
Fracture	Flat regular to uneven
Mohs scale hardness	6.5–7
Luster	Vitreous
Streak	light brown
Diaphaneity	Translucent
Specific gravity	3.9
Optical properties	Biaxial (+)
Refractive index	nα = 1.715 nβ = 1.718 nγ = 1.733
Birefringence	δ = 0.018
Pleochroism	Strong
References	[1][2][3][4]

Dollaseite-(Ce) is a sorosilicate end-member epidote mineral, with the formula CaREE⁺³Mg₂AlSi₃O₁₁F(OH), where cerium is the dominant rare earth element (REE). It also includes lanthanum, neodymium, praseodymium, samarium, and gadolinium, and since cerium is the dominant REE, it is placed in the name and formula. It was first discovered and described by P. Geijer in 1927, in the Ostanmossa mine, Norberg district, Sweden, which is the type locality today. It was first named "magnesium orthite" because of its relation to orthite (orthite being the corresponding end-member rich in iron). When orthite was renamed to allanite in 1986, the Mg end-member was included. Peacor and Dunn redefined the Mg end-member in 1988 as dollaseite, after Wayne A. Dollase, a pioneer in the study of epidote and long-time mineralogy professor at UCLA. This redefinition was necessary because of a different coupled-substitution between clinozoisite-allanite and clinozoisite-dollaseite. The clinozoisite-dollaseite substitution is REE + Mg = Ca + Al and Mg + F = Al + O.

Dollaseite is a metamorphic mineral associated with Västmanlandite-(Ce), Fluorbritholite-(Ce), tremolite, norbergite, and calcite. It is not considered hazardous, but is radioactive because of the REE content. The mineral neotype specimen (NMNH no. R6505) of dollaseite is on deposit at the Smithsonian Institution.

See also

• List of minerals
• List of minerals named after people

References

1. ^ http://www.minsocam.org/ammin/AM73/AM73_838.pdf, Peacor, D.R. and Dunn, P.J., 1988, Dollaseite-(Ce)(magnesium orthite redefined): structure refinement and implications for F + M 2+ substitution in epidote-group minerals. American Mineralogist: 73: 838-842
2. ^ http://rruff.geo.arizona.edu/doclib/hom/dollaseitece.pdf Handbook of Mineralogy
3. ^ http://www.mindat.org/min-1303.html Mindat
4. ^ http://www.webmineral.com/data/Dollaseite-(Ce).shtml Webmineral