Staurolite

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Staurolite
Staurolite-26463.jpg
Staurolite from Pestsovye Keivy, Keivy Mountains, Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia, 2.5 x 2.2 x 1 cm
General
Category Nesosilicate
Formula
(repeating unit)
Fe2+2Al9O6(SiO4)4(O,OH)2 [1]
Strunz classification 9.AF.30
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group C2/m
Unit cell a = 7.86  Å, b = 16.6 Å
c = 5.65 Å; β = 90.45°; Z = 2
Identification
ColorDark reddish brown to blackish brown, yellowish brown, rarely blue; pale golden yellow in thin section
Crystal 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 scale hardness7 - 7.5
Luster Subvitreous to resinous
Streak White to grayish
Diaphaneity Transparent to opaque
Specific gravity 3.74 - 3.83 meas. 3.686 calc.
Optical propertiesBiaxial (+)
Refractive index 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 angle Measured: 88°, Calculated: 84° to 88°
Dispersion r > v; weak
References [2] [3] [4]

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. [1]

Contents

Properties

Staurolite from Madagascar Staurolit, Madagaskar.jpg
Staurolite from Madagascar

Staurolite 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

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. [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

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

Related Research Articles

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. Minerals are most commonly associated with rocks due to the presence of minerals within rocks. These rocks may consist of one type of mineral, or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.

Titanite Nesosilicate mineral

Titanite, or sphene (from the Greek sphenos (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium.

Epidote Sorosilicate mineral

Epidote is a calcium aluminium iron sorosilicate mineral.

Forsterite Olivine, nesosilicate mineral

Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.75 Å (0.475 nm), b 10.20 Å (1.020 nm) and c 5.98 Å (0.598 nm).

Albite feldspar, mineral

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin albus. It is a common constituent in felsic rocks.

Cordierite cyclosilicate, mineral

Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18). A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.

Riebeckite A sodium-rich member of the amphibole group of silicate minerals

Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long prismatic crystals showing a diamond-shaped cross section, but also in fibrous, bladed, acicular, columnar, and radiating forms. Its Mohs hardness is 5.0–6.0, and its specific gravity is 3.0–3.4. Cleavage is perfect, two directions in the shape of a diamond; fracture is uneven, splintery. It is often translucent to nearly opaque.

Fayalite Olivine, nesosilicate mineral

Fayalite (Fe2SiO4; commonly abbreviated to Fa) is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.82 Å, b 10.48 Å and c 6.09 Å.

Cummingtonite Mineral discovered and named after its place of discovery, Cummington, Massachusetts

Cummingtonite ( KUHM-meeng-ton-nyte) is a metamorphic amphibole with the chemical composition (Mg,Fe2+)2(Mg,Fe2+)5Si8O22(OH)2, magnesium iron silicate hydroxide.

Dumortierite nesosilicate mineral

Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al7BO3(SiO4)3O3. Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals. The crystals are vitreous and vary in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.

Illite Group of related non-expanding clay minerals

Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina octahedron (O) – silica tetrahedron (T) layers. The space between this T-O-T sequence of layers is occupied by poorly hydrated potassium cations which are responsible for the absence of swelling. Structurally, illite is quite similar to muscovite with slightly more silicon, magnesium, iron, and water and slightly less tetrahedral aluminium and interlayer potassium. The chemical formula is given as (K,H
3
O)(Al,Mg,Fe)
2
(Si,Al)
4
O
10
[(OH)
2
,(H
2
O)]
, but there is considerable ion (isomorphic) substitution. It occurs as aggregates of small monoclinic grey to white crystals. Due to the small size, positive identification usually requires x-ray diffraction or SEM-EDS analysis. Illite occurs as an altered product of muscovite and feldspar in weathering and hydrothermal environments; it may be a component of sericite. It is common in sediments, soils, and argillaceous sedimentary rocks as well as in some low grade metamorphic rocks. The iron rich member of the illite group, glauconite, in sediments can be differentiated by x-ray analysis.

Lazulite phosphate mineral

Lazulite ((Mg,Fe2+)Al2(PO4)2(OH)2) is a blue, phosphate mineral containing magnesium, iron, and aluminium phosphate. Lazulite forms one endmember of a solid solution series with the darker iron rich scorzalite.

Bixbyite oxide mineral

Bixbyite is a manganese iron oxide mineral with chemical formula: (Mn,Fe)2O3. The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5. It is a somewhat rare mineral sought after by collectors as it typically forms euhedral isometric crystals exhibiting various cubes, octahedra, and dodecahedra.

Lawsonite sorosilicate mineral

Lawsonite is a hydrous calcium aluminium sorosilicate mineral with formula CaAl2Si2O7(OH)2·H2O. Lawsonite crystallizes in the orthorhombic system in prismatic, often tabular crystals. Crystal twinning is common. It forms transparent to translucent colorless, white, and bluish to pinkish grey glassy to greasy crystals. Refractive indices are nα=1.665, nβ=1.672 - 1.676, and nγ=1.684 - 1.686. It is typically almost colorless in thin section, but some lawsonite is pleochroic from colorless to pale yellow to pale blue, depending on orientation. The mineral has a Mohs hardness of 8 and a specific gravity of 3.09. It has perfect cleavage in two directions and a brittle fracture.

Heazlewoodite sulfide mineral

Heazlewoodite, Ni3S2, is a rare sulfur-poor nickel sulfide mineral found in serpentinitized dunite. It occurs as disseminations and masses of opaque, metallic light bronze to brassy yellow grains which crystallize in the trigonal crystal system. It has a hardness of 4, a specific gravity of 5.82. Heazlewoodite was first described in 1896 from Heazlewood, Tasmania, Australia.

Schreyerite (V2Ti3O9), is a vanadium, titanium oxide mineral found in the Lasamba Hill, Kwale district in Coast Province, Kenya. It is polymorphous with kyzylkumite.

Zussmanite (K(Fe2+,Mg,Mn)13[AlSi17O42](OH)14) is a hydrated iron-rich silicate mineral. Zussmanite occurs as pale green crystals with perfect cleavage.

Gedrite Mg-Fe-Mn-amphibole, double chain inosilicate mineral

Gedrite is a crystal belonging to the orthorhombic ferromagnesian subgroup of the amphibole supergroup of the double chain inosilicate minerals with the ideal formula: Mg2(Mg3Al2)(Si6Al2)O22(OH)2

Cleusonite is a member of the crichtonite group of minerals with a chemical formula of (Pb,Sr)(U4+,U6+)(Fe2+,Zn)(Ti,Fe2+,Fe3+)18(O,OH)38. This group of minerals contains approximately thirteen complex metal titanates. The structures of minerals of this group is complicated by frequent fine-scale twinning and metamictization due to radioactive elements. The crichtonite group consists of members of related mineral species of the type A{BC2D6E12}O38 which are characterized by their predominant cations (as seen in crichtonite (Sr), senaite (Pb), davidite (REE + U), landauite (Na), loveringite (Ca), lindsleyite (Ba), and mathiasite (K).

Millerite sulfide mineral

Millerite is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general lack of association with pyrite or pyrrhotite.

References

  1. 1 2 Klein, Cornelis and Cornelius S. Hurlbut, Jr., Manual of Mineralogy, Wiley. 20th ed., 1985, p. 382 - 3 ISBN   0-471-80580-7
  2. http://rruff.geo.arizona.edu/doclib/hom/staurolite.pdf Handbook of Mineralogy
  3. http://www.mindat.org/show.php?id=3753&ld=1&pho= Mindat.org
  4. http://webmineral.com/data/Staurolite.shtml Webmineral data
  5. Simpson, B. (1983). Rock & Minerals. Elsevier. p. 41. ISBN   9780080984117 . Retrieved 17 November 2017.
  6. The Audubon Society Field Guide to North American Rocks and Minerals, Chesterman and knopf.
  7. Fannin County Archives
  8. Virginia State Parks