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Staurolite

Reddish brown to black nesosilicate mineral

Field	Value
name	Staurolite
category	Nesosilicate
image	Staurolite-26463.jpg
caption	Staurolite from Pestsovye Keivy, Keivy Mountains, Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia, 2.5 × 2.2 × 1 cm
formula	Fe2+2Al9O6(SiO4)4(O,OH)2
IMAsymbol	St
strunz	9.AF.30
system	Monoclinic
class	Prismatic (2/m)
(same H-M symbol)
symmetry	C2/m
unit cell	a = 7.86 Å, b = 16.6 Å
c = 5.65 Å; β = 90.45°; Z = 2
color	Dark reddish brown to blackish brown, yellowish brown, rarely blue; pale golden yellow in thin section
habit	Commonly in prismatic crystals
twinning	Commonly as 60° twins, less common as 90° cruciform twins
cleavage	Distinct on {010}
fracture	Subconchoidal
tenacity	Brittle
mohs	7 – 7.5
luster	Subvitreous to resinous
streak	White to grayish
diaphaneity	Transparent to opaque
gravity	3.74 – 3.83 meas. 3.686 calc.
opticalprop	Biaxial (+)
refractive	nα = 1.736 – 1.747 nβ = 1.740 – 1.754 nγ = 1.745 – 1.762
birefringence	δ = 0.009 – 0.015
pleochroism	X = colorless; Y = pale yellow; Z = golden yellow
2V	Measured: 88°, Calculated: 84° to 88°
dispersion	r v; weak
references

(same H-M symbol) c = 5.65 Å; β = 90.45°; Z = 2 | length fast/slow =

Staurolite is a reddish brown to black, mostly opaque, nesosilicate mineral with a white streak. It crystallizes in the monoclinic crystal system, has a Mohs hardness of 7 to 7.5 and the chemical formula: Fe2+2Al9O6(SiO4)4(O,OH)2. Magnesium, zinc and manganese substitute in the iron site and trivalent iron can substitute for aluminium.

Properties

Staurolite often occurs twinned in a characteristic cross-shape, called cruciform penetration twinning. In handsamples, macroscopically visible staurolite crystals are of prismatic shape. The mineral often forms porphyroblasts.

In thin sections staurolite is commonly twinned and shows lower first order birefringence similar to quartz, with the twinning displaying optical continuity. It can be identified in metamorphic rocks by its swiss cheese appearance (with poikilitic quartz) and often mantled porphyroblastic character.

Name

The name is derived from the Greek, stauros for cross and lithos for stone in reference to the common twinning.

Occurrence

Staurolite is a regional metamorphic mineral of intermediate to high grade. It occurs with almandine garnet, micas, kyanite; as well as albite, biotite, and sillimanite in gneiss and schist of regional metamorphic rocks.

It is the official state mineral of the U.S. state of Georgia and is also to be found in the Lepontine Alps in Switzerland.

Staurolite is most commonly found in Fannin County, Georgia. It is also found in Fairy Stone State Park in Patrick County, Virginia. The park is named for a local name for staurolite from a legend in the area. Samples are also found in Island Park, Idaho, near Henrys Lake; Taos, New Mexico; near Blanchard Dam in Minnesota; and Selbu, Norway.

Use

Staurolite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism.

References

Klein, Cornelis and Cornelius S. Hurlbut, Jr., ''Manual of Mineralogy,'' Wiley. 20th ed., 1985, p. 382 – 3 {{ISBN. 0-471-80580-7
Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
http://rruff.geo.arizona.edu/doclib/hom/staurolite.pdf Handbook of Mineralogy
http://www.mindat.org/show.php?id=3753&ld=1&pho= Mindat.org
http://webmineral.com/data/Staurolite.shtml Webmineral data
(1983). "Rock & Minerals". Elsevier.
The Audubon Society Field Guide to North American Rocks and Minerals, Chesterman and knopf.
[http://www.williamlstuart.com/tag/fannin-county/ Fannin County Archives]
[http://www.dcr.virginia.gov/state_parks/fai.shtml Virginia State Parks]

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.

magnesium-minerals iron(ii)-minerals zinc-minerals aluminium-minerals nesosilicates symbols-of-georgia-(u.s.-state) monoclinic-minerals minerals-in-space-group-12

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