STAUROLITE Crystal Cluster Mineral Specimen Fairy Cross KEIVY RUSSIA for Sale

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STAUROLITE Crystal Cluster Mineral Specimen Fairy Cross KEIVY RUSSIA For Sale

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STAUROLITE Crystal Cluster Mineral Specimen Fairy Cross KEIVY RUSSIA:
$34.99

This specimen weighs 7.66 grams. It measures 22 mm x 21 mm x 11 mm.I offer a shipping discount for customers who combine their payments for multiple purchases into one payment!
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and I will buy back the item for your full purchase price. I am selling this really neat Staurolite crystal cluster fine mineral specimen. It is from Keivy, Russia. This specimen is beautifully formed and the crystals are visible from both sides! If you have any questions, do not hesitate to ask me. Have fun offerding, thanks so much for visiting my sale and have a great day!
The following is information about this from wikipedia:StauroliteFrom Wikipedia, the free from Pestsovye Keivy, Keivy Mountains, Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia, 2.5 x 2.2 x 1 cmGeneralCategory NesosilicateFormula(repeating unit) Fe2+2Al9O6(SiO4)4(O,OH)2[1]Strunz classification 9.AF.30Crystal system MonoclinicCrystal class Prismatic (2/m)(same H-M symbol)Space group C2/mUnit cell a = 7.86 Å, b = 16.6 Åc = 5.65 Å; β = 90.45°; Z = 2IdentificationColor Dark reddish brown to blackish brown, yellowish brown, rarely blue; pale golden yellow in thin sectionCrystal habit Commonly in prismatic crystalsTwinning Commonly as 60° twins, less common as 90° cruciform twinsCleavage Distinct on {010}Fracture SubconchoidalTenacity BrittleMohs scale hardness 7 - 7.5Luster Subvitreous to resinousStreak White to grayishDiaphaneity Transparent to opaqueSpecific gravity 3.74 - 3.83 meas. 3.686 calc.Optical properties Biaxial (+)Refractive index nα = 1.736 - 1.747 nβ = 1.740 - 1.754 nγ = 1.745 - 1.762Birefringence δ = 0.009 - 0.015Pleochroism X = colorless; Y = pale yellow; Z = golden yellow2V angle Measured: 88°, Calculated: 84° to 88°Dispersion r > v; weakReferences [2][3][4]Staurolite is a red 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.[1]
Contents [hide]1 Properties2 Name3 Occurrence4 Use5 from MadagascarStaurolite often occurs twinned in a characteristic cross-shape, called cruciform penetration twinning.[5] 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[edit]The name is derived from the Greek, stauros for cross and lithos for stone in reference to the common twinning.
Occurrence[edit]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.[6]
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. [7] 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.[8] Samples are also found in Island Park, Idaho, near Henrys Lake; Taos, New Mexico; near Blanchard Dam in Minnesota; and Selbu, Norway.
Use[edit]Staurolite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism.