spurrite

{{Short description|Nesosilicate mineral}}

{{Infobox mineral

| name = Spurrite

| category = Nesosilicate

| image = Spurrite Calcium silicate and carbonate Luna county New mexico 1873.jpg

| caption = Spurrite from New Mexico

| formula = Ca₅(SiO₄)₂CO₃

| IMAsymbol = Spu{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |s2cid=235729616 |doi-access=free|bibcode=2021MinM...85..291W }}

| molweight =

| strunz = 9.AH.15

| system = Monoclinic

| class = Prismatic (2/m)
(same H-M symbol)

| symmetry = P2₁/a

| color = Gray, gray white to lilac gray

| habit = Massive to granular

| twinning = Polysynthetic twins on [001] and [101]

| cleavage = Distinct on [100]

| fracture = Uneven to splintery

| mohs = 5

| luster = vitreous to resinous

| refractive = nα = 1.640–1.641 nβ = 1.674–1.676 nγ = 1.679–1.681

| opticalprop = Biaxial (−)

| birefringence = δ = 0.039–0.040

| pleochroism =

| streak = White

| gravity = 3

| melt =

| fusibility =

| diagnostic =

| solubility =

| diaphaneity = Transparent to translucent

| other = Green cathodoluminescence

| references = http://rruff.geo.arizona.edu/doclib/hom/spurrite.pdf Mineral Handbookhttp://www.mindat.org/min-3734.html Mindathttp://webmineral.com/data/Spurrite.shtml Webmineral data

}}

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

Spurrite is generally formed in contact metamorphism zones as mafic magmas are intruded into carbonate rocks.Smith, J.V. (1960) "The Crystal structure of Spurrite, Ca₅(SiO₄)₂CO₃". Acta. Cryst. 13, 454 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.Barthemy, D. (2000) Afwillite Mineral Data, (http://webmineral.com/data/Afwillite.shtml)

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.