Spurrite

Spurrite is a white, yellow or light blue mineral with monoclinic crystals. Its chemical formula is Ca5(SiO4)2CO3.[4]

Spurrite
Spurrite from New Mexico
General
CategoryNesosilicate
Formula
(repeating unit)		Ca5(SiO4)2CO3
Strunz classification9.AH.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Identification
ColorGray, gray white to lilac gray
Crystal habitMassive to granular
TwinningPolysynthetic twins on [001] and [101]
CleavageDistinct on [100]
FractureUneven to splintery
Mohs scale hardness5
Lustervitreous to resinous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3
Optical propertiesBiaxial (-)
Refractive indexnα = 1.640–1.641 nβ = 1.674–1.676 nγ = 1.679–1.681
Birefringenceδ = 0.039–0.040
Other characteristicsGreen cathodoluminescence
References[1][2][3]

Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks.[5] Spurrite's space group is P 2/a. It is biaxial with a birefringence of 0.0390–0.0400, giving second order red interference colors when viewed under crossed polarizers in a petrographic microscope.[6]

The calcium is in six-fold coordination with the oxygen, the silicon is in a four-fold coordination with the oxygen and the carbon is in two-fold coordination. One unique characteristic of spurrite is that it actually abides by two twin laws. Polysynthetic twinning can occur along its (001) and another type of twinning can occur parallel to its optical axes.[5]

Discovery and occurrence

Spurrite was first described in 1908 for an occurrence in the Terneras Mine, Velardeña District, Durango, Mexico. It was named for American economic geologist Josiah Edward Spurr (1870–1950).[2]

In addition to its type locality, spurrite has been reported from Riverside County, California; Luna County, New Mexico; and from the Little Belt Mountains, Lewis and Clark County, Montana. It is also found in Ireland, Scotland, New Zealand, Turkey, Israel, Japan and Siberia.[1]

Cement manufacture contaminant

Spurrite forms as contaminating spurrite rings on the walls of cement kilns during the production of Portland cement.[7]

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References
  1. http://rruff.geo.arizona.edu/doclib/hom/spurrite.pdf Mineral Handbook
  2. http://www.mindat.org/min-3734.html Mindat
  3. http://webmineral.com/data/Spurrite.shtml Webmineral data
  4. Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig: Dana's new mineralogy, p. 1106. John Wiley & Sons, 1997
  5. Smith, J.V. (1960) "The Crystal structure of Spurrite, Ca5(SiO4)2CO3". Acta. Cryst. 13, 454
  6. Barthemy, D. (2000) Afwillite Mineral Data, (http://webmineral.com/data/Afwillite.shtml)
  7. Mosci, Ricardo, 1998, How To Eliminate Calcining Zone Rings, Cement America http://cementamericas.com/mag/cement_eliminate_calcining_zone/
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