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Glaucophane

Inosilicate mineral

Field	Value
name	Glaucophane
category	Inosilicates
Sodic amphibole group
image	Glaucophane bleu de Groix.jpg
imagesize	260px
caption	Glaucophane with fuchsite (white oval)
formula	☐Na2(Mg3Al2)Si8O22(OH)2
IMAsymbol	Gln
strunz	9.DE.25
system	Monoclinic
class	Prismatic (2/m)
(same H-M symbol)
symmetry	C2/m
color	Gray, navy blue, lavender-blue
habit	slender long prisms, Massive granular to columnar
cleavage	Good on [110] and on [001]
fracture	Brittle – conchoidal
mohs	6.0–6.5
luster	Vitreous – pearly
streak	Grayish blue
diaphaneity	Translucent
gravity	3–3.15
opticalprop	Biaxial (−)
refractive	nα = 1.606 – 1.637 nβ = 1.615 – 1.650 nγ = 1.627 – 1.655
birefringence	δ = 0.021
pleochroism	Strong
dispersion	Strong
references

Sodic amphibole group (same H-M symbol) | length fast/slow =

Glaucophane is a mineral and a mineral group belonging to the sodic amphibole supergroup of the double chain inosilicates, with the chemical formula Na2(Mg3Al2)Si8O22(OH)2.

Glaucophane crystallizes in the monoclinic system.

Name

Glaucophane is named for its typical blue color. In Greek, glaucophane means "blue appearing". As the major mineral component, it is glaucophane's color that gives the "blueschist" metamorphic rock type its name.

Characteristics

The blue color is very diagnostic for this species. Glaucophane, along with the closely related mineral riebeckite, to which it forms a series with, and their intermediate crossite, are the only well known amphiboles that are commonly blue. Glaucophane forms a solid solution series with ferroglaucophane (). Glaucophane is the magnesium-rich endmember and ferroglaucophane is the iron-rich endmember.

Ferroglaucophane is similar to glaucophane but is slightly denser and hence increased specific gravity. The two endmembers are indistinguishable in hand specimens and are strongly pleochroic. Glaucophane's hardness is 5–6 and its specific gravity is approximately 3–3.2.

Occurrence

The blueschist metamorphic facies gets its name from abundant blue minerals glaucophane and lawsonite. Glaucophane generally forms in blueschist metamorphic rocks of gabbroic or basaltic composition that are rich in sodium and have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone.

This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. Glaucophane is also found in eclogites that have undergone retrograde metamorphism.

Folded Glaucophane Blueschist, [[Syros, Greece

There is also a rare amphibole called holmquistite, chemical formula Li2Mg3Al2Si8O22(OH)2, which occurs only in lithium-rich continental rocks. For many years, holmquistite was mistaken for glaucophane, as the two look identical in thin section.

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
http://rruff.geo.arizona.edu/doclib/hom/glaucophane.pdf Handbook of Mineralogy
http://webmineral.com/data/Glaucophane.shtml Webmineral
"Glaucophane: Glaucophane mineral information and data.".
Burke, Ernst A.J.. "International Mineralogical Association - Commission on New Minerals, Nomenclature and Classification".

Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

sodium-minerals magnesium-minerals iron(ii)-minerals aluminium-minerals amphibole-group monoclinic-minerals minerals-in-space-group-12

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