Editing Labradorite (section)

{{Short description|Feldspar mineral}}
{{Infobox mineral
| name          = Labradorite
| category      = [[Tectosilicate]] [[minerals]], [[feldspar]] [[Mineral group|group]], [[plagioclase]] series
| boxwidth      =
| boxbgcolor    =
| image         = Labradorite polie 3(Madagascar).jpg
| imagesize     = 260px
| caption       = Labradorite in a polished rock slab
| formula       = (Ca,Na)(Al,Si)<sub>4</sub>O<sub>8</sub>, where Na is 30-50% & Ca is 50–70%
| molweight     =
| system        = [[Triclinic]]
| class         = [[Pinacoidal]] ({{overline|1}}) <br/><small>(same [[H-M symbol]])</small>
| unit cell     = a = 8.155&nbsp;[[Ångström|Å]], b = 12.84&nbsp;Å <br/>c = 10.16&nbsp;Å; α = 93.5° <br/>β = 116.25°, γ = 89.133°; Z&nbsp;=&nbsp;6
| color         = Gray, gray-white, brown, greenish, pale green, blue, orange, pink, yellow, colorless
| habit         = Crystals typically thin and tabular, rhombic in cross section, striated; massive
| twinning      = Common by [[albite]], [[pericline]], Carlsbad, Baveno, or Manebach twin laws
| cleavage      = Perfect on {001}, less perfect on {010}, intersecting at near 90°; distinct on {110}
| fracture      = Uneven to conchoidal
| mohs          = 6–6.5
| luster        = Vitreous to pearly on cleavages
| polish        =
| refractive    = n<sub>α</sub> = 1.554–1.563<br/>n<sub>β</sub> = 1.559–1.568<br/>n<sub>γ</sub> = 1.562–1.573
| opticalprop   = Biaxial (+)
| birefringence = δ = 0.008–0.010
| 2V            = Measured: 85°
| dispersion    = None
| pleochroism   =
| fluorescence  =
| absorption    =
| streak        = White
| gravity       = 2.68 to 2.72
| density       =
| melt          =
| fusibility    =
| diagnostic    =
| solubility    =
| diaphaneity   = Translucent to transparent
| other         = Labradorescence ([[iridescence]], [[Lustre_(mineralogy)#Schiller|schiller optical effect]])
| references    = <ref name="HBM">[http://rruff.geo.arizona.edu/doclib/hom/labradorite.pdf Handbook of Mineralogy]</ref><ref name="Mindat">[http://www.mindat.org/show.php?id=2308&ld=1#themap Mindat.org]</ref><ref name="Webmin">[http://webmineral.com/data/Labradorite.shtml Webmineral data]</ref>
}}
[[File:Labrador spektrolit - Ylamaa, Finlandia.jpg|thumb|Labradorite (Spectrolite) – Ylämaa,  Finland.]]
'''Labradorite''' (([[Calcium|Ca]], [[Sodium|Na]])([[Aluminum|Al]], [[Silicon|Si]])<sub>4</sub>[[Oxygen|O]]<sub>8</sub>) is a calcium-enriched [[feldspar]] [[mineral]] first identified in [[Labrador]], Canada, which can display an [[iridescence|iridescent]] effect ([[Lustre_(mineralogy)#Schiller|schiller]]).

Labradorite is an intermediate to calcic member of the [[plagioclase]] series. It has an [[anorthite]] percentage (%An) of between 50 and 70. The [[specific gravity]] ranges from 2.68 to 2.72. The streak is white, like most [[silicates]]. The [[refractive index]] ranges from 1.559 to 1.573 and [[Crystal twinning|twinning]] is common. As with all plagioclase members, the crystal system is [[triclinic]], and three directions of [[Cleavage (crystal)|cleavage]] are present, two of which are nearly at right angles and are more obvious, being of good to perfect quality (while the third direction is poor). It occurs as clear, white to gray, blocky to [[lath]] shaped grains in common [[mafic]] [[igneous rocks]] such as [[basalt]] and [[gabbro]], as well as in [[anorthosite]]s.