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Staurolite

Posted by Olav Revheim  
Staurolite
May 15, 2013 08:26PM
    
First Draft


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Staurolite
(Fe2+)2Al9Si4O23(OH)

Staurolite 8 cm specimen, Kola Peninsula, Russia ©


Staurolite is a typical mineral of metamorphic rocks originating from Al-rich, argillaceous sediments, i.e. mica schist and sometimes gneiss. Occasionally, it can also be found in metavolcanic rocks. It is a widespread mineral, formed by regional metamorphosis as well as in contact aureoles around intrusions. Staurolite is a typical mineral of medium grade metamorphosis, and is often used as an index mineral for determining the pressure and temperature conditions of the metamorphic event(s). It is commonly associated with almandine and/or kyanite, which are formed under the same conditions as staurolite.

Being a metamorphic mineral, staurolite is often replaced by other minerals. In prograde conditions, sillimanite pseudomorphs after staurolite are known from Virginia, USA, but retrograde alteration to mica pseudomorphs are common from many places around the world. Staurolite also shows oriented intergrowths with muscovite and with kyanite. The Pizzo Forno specimens are rather impressive examples of the latter. Staurolite shows a wide variety of twins and trillings. 60o and 90o crosses are most sought after, and often used as pendants. In rare cases, staurolite can be transparent, and suitable for cutting to deep reddish-brown gems rarely larger than 1 ct.

Staurolite crystals with rough and pitted surfaces are common, due to inclusions of mica, garnet or other minerals that are included in the staurolite and that may or may not be removed during cleaning. The rough surface may also be the result of weathering of the crystals, as the staurolite structures are more resistant to pitting in some parts of the molecule than others. Sometimes this creates oriented pits, resembling striations.

Since staurolite crystals are often embedded in mica-schist, abrasion tools are commonly used to expose the staurolite crystals within the matrix. It appears that the temptation to "improve" the surface of pitted or included crystals is sometimes hard to resist. Fakes are also known, where "staurolite" crosses are carved out of suitable material (talc-schist) and treated with oil to get the deep brown colour so typical for this mineral.

Fake staurolite, hardness at ~2, SG at 2.5© Bill Cordua
One of these is fake, the rest are from
the Blanchard Dam, Minnesota, USA
© Bill Cordua


The staurolite molecule also accepts atoms other than those listed in the idealized formula. A Fe2+ <->Mg substitution is common, but Mg is rarely dominant. Magnesiostaurolite is listed only from 5 localities in the Mindat database, and is only formed under high pressure (higher than the staurolite stability field) and in rocks with a high Mg/Fe ratio (i.e. mafic granulite facies rocks) together with pyrope. Fe2+ may also be substituted by Zn and, in rare cases, staurolite may be Zn-dominant, forming the mineral zincostaurolite (listed from 5 localities in Mindat). Zincostaurolite appears to be stable within the same P/T regimes as staurolite, and its rarity is due to the normally low Zn/Fe ratio in staurolite forming environments.

The staurolite molecule does not seem to accommodate significant amounts of Mn, which commonly replaces Fe2+ in many other minerals. Staurolite is, however, one of the very few silicates found in nature that can accommodate significant amounts of Co. Lusakite is a Co-bearing variety known from Lusaka, Zambia. A green Cr-bearing variety of staurolite is known from Fiordland, New Zealand.

The best staurolite specimens are those from huge deposits on the Kola peninsula, where single crystals, twins and trillings are known on the market, sometimes associated with almandine and kyanite.

Staurolite
Australia
Queensland, Mount Isa - Cloncurry area, Mary Kathleen district, Cattle Creek

Staurolite 3 cm crystal© Ryan Eagle


The staurolite locality lies about 1.6 km farther on (Wee McGregor) after crossing Cattle Creek, and staurolite crystals up to 8 cm can found on the ground, sometimes also as “maltese crosses” weathered free from the mica schist hosting the crystals. The host schist belongs to the “White Blow” formation, part of the Mount Albert Group of the Mount Isa inlier. This appears to be the only area where this formation is known to carry staurolite. For those who have access to the Australian Mineralogist, the following article would probably provide more information on the locality: Petersen, O.V. and McColl, D. 1982. Staurolite trillings from Cattle Creek, Queensland, Australia. Australian Mineralogist 38 pp 207-208.

References:

Sayab, Mohammad (2005): N-S shortening during orogenesis in the Mt Isa Inlier: the preservation of W-E structures and their tectonic and metamorphic significance. PhD thesis, James Cook University.

Australian Stratigraphic Units database.

Queensland Government, Department of Natural Resources and Mining. Fossicking guide.


Staurolite
Australia
Tasmania, King Island

Staurolite 25 mm crystals© R. Bottrill 2007


Some muscovite - staurolite - quartz schist with black staurolite crystals up to 1 inch in length was observed in the Reekara road area.

References:

Anthony Jannink (1969): Report on exploration licenses 4/69 and 5/69 King Island, Tasmania.

Berry, R.F., Holm, O. and Steele, D.A., (2005): Chemical U-Th-Pb monazite dating and the Proterozoic history of King Island, southeast Australia. Australian Journal of Earth Sciences, 52: 461-471.


Staurolite
Brazil
Minas Gerais, Jequitinhonha Valley, Rubelita,

Staurolite 4.1 cm crystal© Rob Lavinsky



Staurolite
Brazil
Minas Gerais, Jequitinhonha Valley, Rubelita, Fazenda Gramiais

Staurolite >5 cm crystal©


The staurolite from Fazenda Gramais is described as “stout 60o twins”, but I have not been able to find the maximum size of the crystals.

Staurolite-bearing rocks in the Rubelita region belong to the Salinas Group. Near Rubelita, this group mainly contains schists, with quartzite in the south and a metaconglomerate marker unit in the northwestern part. The schists are locally rich in staurolite. Staurolite in the area has formed both through regional geological processes and near the contacts of intruding pegmatites belonging to the Coronel Murta field. The occurence of staurolite in these contact zones is related to the depth of the intrusion in crustal levels (12-15 km), which is deeper than in the Itinga field (5-10 km) further east, where andalusite has formed in those contact zones.

These rocks belong to the Araçuaí Fold Belt, which was developed in the Brasiliano Cycle,1000 to 450 Ma ago. Several schist formations in this fold belt, from Bahia through the whole of Minas Gerais, contains staurolite. These are often small mm-sized grains, but locally larger crystals can be found, such as at:

- Tapera do Rochedo, Bahia, where crystals to 10 cm have been found, sometimes altered to muscovite.
- Agua Quente, Rio Pardo de Minas, Minas Gerais, where crystals to 2 1/2 inches have been found
- From J.C.Oakenfull (1912): Valle da Ribeira (Sao Paulo) and in the mica schist of Arussuahy, in crystals up to 3/4 - 2 inches. Forms a great part of the schists some 20 miles from Ouro Preto, also at Franca (Sao Paulo).

The exact localities of specimens acquired in the mineral trading centers of Brazil can be difficult to ascertain.

References:

J.C.Oakenfull (1912): Brazil in 1911.

A.C. Pedrosa-Soares, M. Chaves, R. Scholz (2009): Field Trip Guide, Eastern Brazilian Pegmatite Province, PEG2009 - 4th International Symposium on Granitic Pegmatites.

A. C. Pedrosa-Soares & F. F. Alkmim (2011): The Brazilian counterpart of the Araçuaí-West Congo orogen. Field trip guide. Gondwana 14, Brazil.

Rui L.B.P Monteiro, Othon H. Leonardos, Jose Marques Correi A-Neves (1990): An epigenetic origin for the new scheelite and wolframite occurrences in the middle Jequitinhonha Valley, Minas Gerais, Revista Brasileira de Geociências 20(l-4):68-74.


Staurolite
Bulgaria
Haskovo Oblast (Khaskovo Oblast), Topolovgrad Obshtina, Oreshnik

Staurolite 6 cm specimen© Marcus V.
Staurolite 12 cm specimen© Marcus V.

Staurolite occurs with almandine garnets (up to 0.2 cm) in fine grained, dark grey quartz-mica schists to the south of the village Oreshnik . The dark brown staurolite crystals have been observed in sizes up to 12 x 3 x 1.8 cm (Tzankova 2005). They are prismatic in habit and show pseudohexagonal basal sections, and twins are common. In thin section, the staurolite has abundant inclusions of quartz, garnet, biotite and ilmenite. Staurolite is not found as inclusion in garnet, but garnet is frequently observed as inclusion in staurolite.

The staurolite-bearing rocks belong to the Ustrem Formation (Topolovgrad Supergroup), which is represented by: a) quartz-mica schists containing porphyroblasts of biotite, garnet and staurolite; b) garnet-amphibole, epidote-zoisite and quartz-amphibole schists; c) calc-schists; and d) white, grey and striped marbles.

References:

Nikoleta Tzankova (2005): Chemical characterization of garnet and P-T conditions of metamorphism of the triassic rocks occuring to the south of Oreshnik, south-east Bulgaria. Annual of the university of mining and geology "St Ivan Rilski", Vol. 48, Part I, Geology and Geophysics.


Staurolite
Canada,
Ontario, Frontenac Co., Clarendon Township


Staurolite 2.2 cm specimen© Maggie Wilson


Staurolite occurs in a 25 mile-long, but rarely more than 100 yards wide, band of meta-pelitic Grenville schist. The metamorphic grade of the schist increases from chlorite grade in the southwest through kyanite/staurolite to sillimanite in the northeast. Staurolite can be found across most of the distance, but according to Hounslow (1965) mostly as anhedral, heavily included porphyroblasts up to 6.4 mm. The best crystals are reported by Hewitt (1952), who found well-formed crystals from ¼ to 2 inches in an outcrop 1/2 mile east of the Fernleigh post office, together with large kyanite crystals in a fine grained, sheared sericite-sillimanite-quartz schist. According to Festa (2012), the area is not easily accessible today.

References:

B. L. Smith (1951): Preliminary report on the geology of Clarendon Township, Frontenac County.

D.F.Hewitt (1952): Kyanite and Sillimanite in Ontario, Ontario Department of Mines. Industrial Mineral Circular. No. 4.

A.W.Hounslow (1965): Chemical Petrology of some Grenville schists near Fernleigh, Ontario.

Frank Festa (2012): 12. Exploring Former Mining Sites From Kaladar to Fernleigh, Ontario, Canada. Mindat article.


Staurolite
Czech Republic
Moravia (Mähren; Maehren), Olomouc Region, Šumperk (Mährisch Schönberg), Nový Malín

Staurolite 11 cm specimen© Petr Gadas


Staurolite crystals up to 6 cm can be found either weathered free from the host rock or embedded in mica schist with garnets. The mica schist is of metamorphosed Devonian sediments belonging to the Silezicum domains of the Bohemian massif. The locality lies in a Nature Reserve.

In addition to this locality, Kretschmer (1912) describes a site south of Šumperk, where large prismatic staurolite crystals occur with magnetite octahedrons up to 2 cm in the contact zone between a staurolite-mica schist and a diorite-like intrusion. The staurolite occurs as single crystals as well as 60o and 90o twins.

References :

Czech Geological Survey, Šerák-Keprník, Geological localities, [lokality.geology.cz].

Franz Kretschmer (1912): Die Petrographie und Geologie der Kalksilikat-felse in der Umgebung von Mähr.-Schönberg., Jahrbuch der Kaiserlich-Kȍniglichen Geologichen Reichsanstalt, Band 62, pp 43-53.

Petr Černy, Milan Novak, Ron Chapman (1992): Effects of sillimanite grade metamorphism and shearing on Nb-Ta oxide minerals in granite pegmatites: Mariškov, Northern Moravia, Czechoslovakia.


Staurolite
France
Brittany, Finistère, Briec, Landudal, Langelin brook alluvials

Staurolite ca. 10 cm crystal ©



Staurolite
France
Brittany, Finistère, Coray

Staurolite 25 mm crystal © Rui Nunes 2008
Staurolite 25 mm crystal © Rui Nunes 2008

Staurolite has long been known from Brittany. Since these localities have continuously provided specimens since the Middle Ages and before, the text entry is more extensive than for some other localities.

Prior to the more scientific description of staurolite, one of its common local names was “Croisette de Bretagne”. Lacroix (1893), in his famous “Mineralogie de la France”, quotes Christophe-Paul.G de Robien (1751) as being the first to give a scientific description of staurolite in his essay on three different species of figured stone, namely staurolite twins, chiastolite and pyrite cubes. (Dissertation sur la formation des trois differentes especes de pierre figurees qui se trouvent dans la Bretagne) from his book “Novelles idees sur la formation des Fossiles”. Robien describes Scaer, Baud and Plumelin as localities for this “pierre de croix” - the name he used for staurolite. These localities continue to produce staurolite specimens today.

The cross-shaped rocks that were (and still are) found in the soil have, understandably, stimulated peoples' imagination. There are many legends surrounding these “pierre de croix”. In one story, the Count of Trévalot built a chapel on top of a pagan temple to thank God for a victory against a rival. Soon after, miracles started to occur at the site. Centuries later, the chapel was set on fire as its forces were blamed for a famine. After the fire, a heavy storm occurred and a shower of cross-shaped stones fell on the site of the chapel, reminding everyone that the chapel was built in the memory of Christ. This legend comes in many variations, and is one of many.

Today, of course, the general understanding is that the cruciform crystals found in the soil come from the earth’s crust rather than from above. Staurolite is found in irregular patches of mica schists in a narrow band between Baud and Coray, and also as loose crystals in the soil (in farm fields), ravines and creeks. Lacroix (1893) gives a detailed account of several localities in this area. The staurolite zone runs roughly parallel to the South Armorican shear zone. Baud lies just north of this shear zone, and Coray a little further north and some 70 km further west. Scaer is another well known locality between these two places. The staurolite-bearing mica schists belong to the Central Armorican Domain, representing a Palaeozoic basement microplate wedged on top of the blueschist facies subduction zone of Gondwana (Variscan orogeny ~350-370 million years ago). The Central Armorican domain has only been subjected to low grade regional metamorphism (maximum greenscist facies). Staurolite has formed in the contact aureole around later intruding granites (~290 Ma), hence the occurrence of staurolite in patches of mica schist in a narrow band near the shear zone. The staurolite may be associated with crystals of other species, such as kyanite, andalusite and garnet, indicating the conditions of metamorphosis at the various localities.

The best description of the crystals still appears to be the one given by Lacroix (1893). He states that both size and shapes of the crystals vary within and between the different localities, some of the largest coming from Baud (up to minimum 7.5 cm) and Coray, Scaer and Coadrix, where crystals exceeding 10 cm were found. Twins are relatively rare, but they are most sought after and have been sold as souvenirs for hundreds of years. Both 60o and 90o twins are known, often with different sizes between the two crystals. Trillings are very rare. Inclusions of quartz, garnet and mica are common.

Lacroix also describes a locality near Mur en Plouigneau, where staurolite occurs in a shale rich in organic matter. Here the staurolite contains zones and patterns mirroring crystal structure.

References:

A.Lacroix (1893): Mineralogie de la France et de ses colonies.

Michel Ballevre, Valerie Bosse, Celenie Ducassou, Pavel Pitra (2009): Paleozoic history of the Armorican Massif, Model for the tectonic evolution of the suture zones, Comptes Rendus Geoscience, Vol. 341, pp 174-201.

Gérard M. Stamp, Jürgen F. von Raumer, Gilles D. Borel (2002): Paleozoic evolution of pre-Variscan terranes: From Gondwana to the Variscan collision, Geological Society of America Special Paper 364.


Staurolite
France
Brittany, Morbihan, Baud

Staurolite 7 cm crystal © Yves Masson



Magnesiostaurolite
Italy
Piedmont, Cuneo Province, Dora Maira Massif, Varaita Valley

Magnesiostaurolite FOV 1.5 mm© Roberto Bosi


Magnesiostaurolite is a very rare mineral, known from only a handful localities (5 listed on mindat). It occurs exclusively in metamorphic ultra high-pressure (UHP) rocks. Lab experiments show that the mineral has no stability field below 12 kbar (common Fe-dominant staurolite is stable down to 1 kbar pressure). It was first identified in a metamorphosed ultra-mafic pebble from Fiordland, but the type description was on material from the Gilba Valley in Italy, which is considered the type locality.

These rocks belong to the Dora Maira Massif and is metamorphosed at temperatures in the 600–800°C range and at pressures somewhere between 25-40 kbar. The magnesiostauriolite was first found as μm-sized (from a few tens to 250 µm across) anhedral inclusions in pyrope in metapelitic rocks, but was later been found as up to 1 cm yellow, deep yellow to brown crystals from outcrops near Venasca, Martiniana Po and in the Gilba Valley,

References:

Roberto Bosi (2013): Personal communication.

P. Ambrino and P Brizio (2008): I MINERALI DI UHPM Metamorfismo di altissima pressione dell’ unità BROSSASCO-ISASCA (CUNEO), Macro-Micro, Associazione Piemontese di Mineralogi e Paleontologia, anno 2008 Numero 9.

Christian Chopin and Hans Peter Schertl (1999): TheUHP Unit in the Dora-Maira Massif, Western Alps. International Geology Review. Vol.41. p.765-780.


Staurolite
Namibia
Erongo Region, Swakopmund District, Namib Naukluft National Park, Gorob Mine

Staurolite 4.2 cm crystal © Rob Lavinsky


The abandoned Gorob mine is one of many similar Cu-Zn-Ag deposits. These deposits are volcanogenic massive sulphide (VMS) deposits hosted by the Kuiseb Formation, a sequence of quartz-plagioclase-mica schists found in close proximity with the 0.5 to 3 km wide and 350 km long linear Matchless Amphibolite Belt. Staurolite is found in strongly foliated and folded Al-rich schists within the Kuiseb Formation. Staurolite as individual crystals to minimum 5 cm as well as twins are found in outcrops near the ore body.

References:

Philo Schoeman (1996): Overview and comparisation of Besshi-type deposit: Ancient and recent. Masters Dissertation, Rhodes University, Department of Geology.

Bruce Cairncross (2004): Field Guide to Rocks & Minerals of Southern Africa, Struik Publishers.


Staurolite
Portugal
Porto District, Gondomar, Fânzeres

Staurolite 40 mm crystal © Rui Nunes 2008


This locality is a small, but very rich locality. It lies in the middle of a village and the schist is partly built over. However, it is an interesting locality with individual crystals up to 7cm as well as cruciform twins. More complex twins and trillings involving 2, 3 and 4 crystals are known. The staurolite is found in pelitic schists, metamorphosed by intrusives during the variscan orogeny. This locality is formed in the same event, and with very similar geology and petrology than the more well known localities in Brittany, France.

References:

Rui Nunes (2013): Personal communication.

Fernandes; J.P., Chaminé, H.I., Borges, F.S. (1998): Considerações sobre o possível significado de marcadores cinemáticos na unidade dosXistos de Fanzeres (Porto, Portugal). GEOlogos 2, 4ª Conferência GGET, Universidade do Porto, 153-156.


Staurolite
Russia
Northern Region, Murmanskaja Oblast', Kola Peninsula, Keivy Mountains

Staurolite 8.7 cm specimen © John Sobolewski

Staurolite 4 cm specimen © Dan & Diana Weinrich Minerals
Staurolite 28 mm crystal © 2009 Michael C. Roarke

If there is a single best locality for staurolite, the Keivy Mountains would probably be it. Staurolite is found as individual crystals (up to 20 cm), twins (heart shaped, 60o and 90o twins) as well as trillings up to 8 cm across embedded in a fine grained mica schist that is often sand blasted away to expose the well-formed staurolite crystals.

Although the Keivy Mountains are normally listed as one locality, the 200 km long and up to 1 km thick metasedimentary and metavolcanic Keivy Group fold belt hardly qualifies as a single locality. Staurolite is found in several of the metamorphic units within the Keivy Group, and is normally associated with high-Al kyanite schists. A rich kyanite schist in this district ranges from 80 to 150 m in thickness and extends for 140 km. Three grades of kyanite schist are recognized: 1) rich ores containing more than 40 percent kyanite, 2) medium-grade ores containing 30-40 percent kyanite, and 3) lean ores containing less than 20 percent kyanite . Voytekhovsky and Neradovsky list 23 kyanite deposits with possible economical potential and most, if not all, of these have associated staurolite schists.

Voytekhovsky and Neradovsky have given an overview of the petrology of the schists in the Shuururta deposit, mapping a more than 50 m thick horizon of "staurolite porphyroblastic schists”. Alexandrov et al. (2007) describe how “tremendous concentrations” of “lumps of huge crystals of blue kyanite, cruciform twins of staurolite and giant garnet crystals are the pride of collectors.” They also show photos of staurolite specimens together with schist outcrops in a barren (but beautiful!) tundra landscape.

The tectonic origin and age of the staurolite schists are debated, but it appears that they are metamorphosed to amphibolite facies from sediments originating from 2.8-2.4 GA old intrusives, and that they are older than the 1.9 to 2.0 GA intrusives belonging to the Lapland-Kola orogeny, although single grain muscovite 40Ar/39Ar age data indicates that mica may have re-crystallised as late as 1.5-1.6 GA age.

References:

Suzanne Herting-Agthe (2004): A new trilling of Staurolite, 22 - Bull. Liaison S.F.M.C. - Vol.16, Le 5ème congrès international “Mineralogy & Museums” (MM5) à Paris.

de Jong K., Ruffet G., Marker M.(2012): Ar/Ar age data of muscovite from the Keivy Terrane (central Kola Peninsula, arctic European Russia) imply a prolonged fluid-assisted recrystallisation.Geophysical Research Abstracts, 14, (EGU General Assembly 2012).

G.Alexandrov, I. Zaitseva, K. Kobyakov, V. Kikhashev (2007): Nature and natural resources of the Murmansk Region , Kola Biodiversity Conservation Centre publication.

D.V. Rundqvist, C. Gillen (editors) (1997): Precambrian Ore Deposits of the East European and Siberian Cratons, Developments in Economic Geology, 30.

Yu.L. Voytekhovsky and Yu. N. Neradovsky (2012): Kyanite of the Bol'shiye Keivy as a complex raw material. Proceedings of the MSTU, Vol. 15, No. 2 pp.439-448.


Staurolite
Russia
Northern Region, Murmanskaja Oblast', Kola Peninsula, Keivy Mountains, Pestsovye Keivy

Staurolite 6.2 cm specimen
Staurolite up to 6 cm crystals © Rob Lavinsky

Staurolite 5.7 cm specimen © Rob Lavinsky
Staurolite 6 cm specimen © Joseph A. Freilich

Staurolite 7.5 cm crystal © Joseph A. Freilich
Staurolite 4.4 cm specimen © David J. Eicher


Staurolite
Russia
Northern Region, Murmanskaja Oblast', Kola Peninsula, Keivy Mountains, Western Keivy Massif, Ploskaya Mt.

Staurolite 5.5 cm crystal © B.Z. Kantor



Staurolite
Switzerland
Ticino (Tessin), Leventina, Chironico Valley, Sponda Alp - Pizzo Forno

Staurolite
, 5 cm FOV
© 2007 Peter Cristofono
Staurolite 2.75 cm crystal © Rob Lavinsky

The staurolite from this locality already was described in detail by Dr Adolf Kenngott (1866) in his “ Minerale der Schweiz”. He gives a rather good description on the exact whereabouts of the locality: “Nach der Mittheilung des Herrn Professor B. Studer musste als genauer Fundort der schonen Staurolith-Krystalle von da die Alpe Sponda auf der Sudseite des Pizzo Forno oberhalb Giornico angegeben werden…… Wahrscheinlich kommen in dem Schiefer, der in der Kette zwichen dem Leventiner und Lavizzarathal lagert an mehreren punkten Staurolith vor."

Staurolite is found in an occasionally quartz-rich, greyish to yellowish white muscovite-rich mica schist, together with darker mica, brownish garnets and rarely black tourmaline. It is, however, the combination specimens with sharp, well formed staurolite and light blue, transparent kyanite crystals that create mineral specimens with a beauty almost unheard of for common rock-forming minerals.

The staurolites are mostly single, reddish to dark brown tabular prismatic crystals, sometimes translucent on the edges. Smaller crystals may be transparent, and then deep brownish red. Twins are rare, and then mostly 60o crosses. 90o twins are very rare. Please see Kenngott (1866) for details on crystals shapes and twin angels.

Of particular interest are the staurolite-kyanite epitaxial intergrowths that can be found in some crystals, such as some of the ones in the right hand photo above. Kenngott (1866), Wenk (1980) and Cesare and Grobety (1995) all describe these crystals. These intergrowths provide a very clear illustration of the close chemical relationship between kyanite and staurolite, where the latter consists of Al2SiO5 units similar to those found in kyanite, but with additional layers of an approximate Al0.7Fe2O2(OH)2 between each kyanite unit.

Although rare in collector grade crystals, such intergrowths are not uncommon, in particular in rocks of multiple metamorphic events with staurolite replacing kyanite or vice versa. The staurolite-bearing mica schists in this area are hosted in the Campo Tencia unit of the Simano Nappe. The Simano Nappe records a complex tectonic evaluation during and after the Tertiary Alpine collision. Allaz et al. (2005) identify 5 metamorphic events, with the Alpine collision as the first. Staurolite has been formed during the second and third metamorphic events in metapelitic mica schists. A more detailed account of the metamorphic history of the staurolite-bearing mica schists can be found in Allaz et al.

References:

Adolf Kenngott (1866): Minerale der Schweiz nach ihre Eigenschaften und Fundorten, Verlag von Vilhem Engelman.

Hans-Rudolf Wenk (1980): Defects along kyanite-staurolite interfaces, American Mineralogist, Volume 65, pages 766-769.

Bernado Cesare and Bernard Grobety (1995): Epitaxial replacement of kyanite by staurolite: A TEM study of the microstructures, American Mineralogist, Volume 80, pages 78-86.

Julien Allaz, Xavier Maeder, Jean-Claude Vannay and Albrecht Steck (2005): Formation of aluminosilicate-bearing quartz veins in the Simano nappe (Central Alps): structural, thermobarometric and oxygen isotope constraints, Schweizerische Mineralogische und Petrographische Mitteilungen 85, 191–214.


Staurolite
USA
Connecticut, Hartford Co., Glastonbury, Diamond Lake locality

Staurolite 7 cm label © 2010 Peter Cristofono
Staurolite 63 mm crystal © 2011 Harold Moritz

Relatively large staurolite crystals, both as individuals and twins, were found along the gas pipeline southwest of Diamond Lake. The staurolite was found in a narrow NW/SE trending band with several different schist units of Middle to Upper(?) Ordovician age. They are regionally metamorphosed within the staurolite stability area. Similar schists belonging to different stratigraphic units can be found on both sides of the Glastonbury gneiss, and staurolite is described from several localities. It appears that the Diamond Lake locality has produced some of the best crystals in the area .

References:

USGS, online geology map and formation descriptions.

Norman L. Hatch (1988): The Bedrock Geology of Massachusetts, USGS Professional Paper 1366 A-D.


Staurolite
USA
Georgia, Fannin Co.

Staurolite Up to 1 in. crystals © Rockpick Legend Co.


Staurolite was named the Georgia State mineral in 1976. It occurs almost exclusively in the northernmost part of the state, in the southern Appalachian Mountains. Fannin County probably hosts the best occurrences.

The area contains metasedimentary and metavolcanic rocks consistent with an island arc environment, of probable Taconian age. The rocks are of variable metamorphic grade, and multiple formations within the Blue Ridge Formation, Bill Arp thrust sheet, Great Mountain Group and the Ocoee Supergroup contain staurolite-bearing schists.

Most of the Fannin County bedrock lies within the staurolite isograd, and multiple localities with collector quality specimens are known. The staurolite zone roughly follows the highway from Blue Ridge through Mineral Bluff, continuing in the same direction into South Carolina.

References:

Breana A. Felix (2012): P-T conditions of selected samples across the Blue Ridge Province. Master's thesis, Marshall University.

USGS online spatial data, Geologic map.

Jeffrey B. Connelly and R.D. Dallmeyer (1993): Polymetamorphic evolution of the Western Blue Ridge: Evidence from 40Ar/39Ar Whole Rock slate/phyllite and muscovite ages. American Journal of Science, Vol. 293, pp 322-359.


Staurolite
USA
Georgia, Fannin Co., Blue Ridge, J. Fred Hackney property

Staurolite 2.7 cm crystal © Van King
Staurolite 2 cm crystal © Van King

Staurolite 2 cm crystal © Van King
Staurolite 2 cm crystal © Ferdinando Giovine

The Fred J. Hackney Farm is the most well known of the Georgia staurolite localities. It used to be a fee-collecting site, but appears now (since 2007) to be closed due to urban development. The staurolite crystals are weathered free from the host rocks and are found by sifting the creek gravel for crystals. During development work in the area, crystals could also be found in their schist host rock. The crystals do not appear to get much larger than an inch (2.5 cm), but may get up to 5 cm. The staurolite shows a wide variety of twins and triplets, but single crystals were nevertheless most common. Staurolite from this locality has been used by Velbel et al. (1996) for investigations on staurolite weathering and by Hubst et al. (1956) for studies on staurolite twins. The latter also shows drawings of multiple twin forms from the Hackney farm.

References:

Various field trip blogs, including “Saying goodbye to the Hackney Farm”.

Michael A. Velbel, Charles L. Basso and Michael J. Zieg (1996): Weathering of staurolite: Crystal-surface textures, relative stability and the rate determining steps. American Journal of Science, Vol. 296, pp 453-472.

Vernon J. Hurst, J.D.H. Donnay and Gabrielle Donnay (1956): Staurolite twinning. Mineralogical Magazine Vol. 31, no. 233, pp 145-163.


Staurolite
USA
Idaho, Benewah Co., Carpenter Creek

Staurolite 4.6 cm crystal ©


In Benewah County, abut 5 miles up Carpenter Creek from it’s junction with the St. Maries River, an extensive ledge of mica schist belonging to the Wallace formation occurs. The ledge lies from the northeast to the southwest and outcrops where it has been cut by a forest road and the creek. Staurolite crystals occur in abundance in the schist, some an inch to 1 1/2 in. length. Many of them are twinned, and a few of the twin crystals are interpenetrated at right angles, forming a natural cross.

References:

John A. Beckwith (1972): Gem Minerals of Idaho, Caxton Printers .

James G. Evans and Phillip R. Moyle (2006): U.S. Industrial Garnet, USGS Bulletin 2209–L.


Staurolite
USA
Maine, Cumberland Co., Windham

Staurolite 1 in. ruler ©


Staurolite from this locality is found in the meta-pelitic Windham Formation, sediments that accumulated in an ocean basin during the late Ordovician to Silurian before they where metamorphosed around 400 Ma. The Windham Formation forms three belts running north-east to south-west, but only the area around South Windham has staurolite bearing rocks. Hussey (1996) gives a good overiew of the extent of the Windham Formation and the stability fields of the different metamorphic minerals. He also provides an in-situ photograph of a staurolite schist resembling the pictured staurolite specimen from Dundee Falls, Presumpscot River. Staurolite twins can be found here, but I have not been able to find any information on the maximum crystal size.

Reference:

Arthur M. Hussey (1996): Bedrock Geology of the North Windham 7 1/2’ Quadrangle, Maine, Department of Conservation, Maine Geological Survey, Open File No. 96-16.


Staurolite
USA,
Minnesota, Morrison Co., Royalton, Blanchard Dam


Staurolite 3.8 cm crystal ©


Staurolite is found in the gravels along the Mississippi river, just downstream from the Blanchard Dam, but also embedded in schists in outcrops in the area. Crystals can be up to about 4 cm. Most are single crystals, but both 60o and 90o twins can be found.

The schist belongs to the Little Falls Formation of the 1.7 GA old Penokean orogeny. The Little Falls Formation crops out sporadically over a large area in southern Morrison County and northeastern Stearns County. It consists predominantly of argillaceous material, metamorphosed to slate, phyllite or finely crystalline schists, interpreted by Holm et al. as metamorphosed continental margin rocks. Due to the few outcrops, it is hard to define the boundaries of the staurolite stability field here, as Holm et al. described staurolite also from other localities.

References:

Bill Cordua: Minnesota twin crystals.

G.B. Morey (1978): Lower and Middle Precambrian stratigraphic nomenclature for East-Central Minnesota. Report of investigations 21, Minnesota Geological Survey.

D.K. Holm, D.A. Schneider, S.Rose, C. Mancuso, M. McKenzie, K.A. Foland, K.V. Hodges (2007): Proterozoic metamorphism and cooling in the southern Lake Superior region, North America and its bearing on crustal evolution, Precambrian Research, Vol.157, pp 106-126.


Staurolite
USA
New Hampshire, Grafton Co., Lisbon, Pond Hill locality (Pearl Lake locality; Mink Pond locality)


Staurolite 2.7 cm crystal © 2005 Peter Cristofono
Staurolite 2 cm crystal © 2005 Peter Cristofono

Staurolite 2 cm crystal © 2006 Peter Cristofono
Staurolite 2 cm crystal © 2007 Peter Cristofono

Staurolite 9.4 cm specimen © Henry Minot 2008

The oldest reference I have found to this locality is from the Grafton County Gazetteer from 1866: " The most characteristic rock…is an argillaceous and micaceous schist filled with staurolite. The best localities of this mineral are in the towns of Lisbon, Enfield and Grantham, where cruciform crystals are quite common.” By 1894, it was a well-known locality, as presented by Penfield and Pratt: "The material from Sugar Hill in Lisbon, N. H., was collected in the summer of 1893 by Professor Brush. As observed by him, extensive ledges of gray staurolitic mica schist occur, extending several miles north from Pearl Lake, better known as Mink Pond, and including the ledges on Garnet Hill and Co wen Hill. In the ledges on Cowen Hill unusually large and fresh crystals are found measuring up to 115 mm. long by 40 mm. broad. Thin sections of these crystals revealed the fact that they are remarkably free from inclusions of quartz and garnet, which are so common in staurolite, but they contain carbonaceous material arranged in certain definite planes

Today, cruciform crystals are not common, but staurolite crystals are still rather abundant, as Mulvey describes in his 2005 field trip report: “Occasionally we encountered crumbly schist with staurolite crystals. While we were on the lookout for the classic staurolite twin which form a cross, we found many very nice samples of single crystals, many with a small (2-3 mm) garnets attached. Chipping the staurolite out of the schist is trickier than it appears! The schist seems to want to break where the crystals form. I ended up taking some nice slabs to 12 inches square with several nice examples instead of trying to break the individuals out on small matrix pieces.”

References:

Joe Mulvey (2009): Mink Pond, New Hampshire, Staurolite & Garnet Deposit.

Hamilton Child (1886) PART FIRST. GAZETTEER Grafton County, N. H. 1709-1886.

S.L. Penfield and J.H. Pratt (1894): On the chemical composition of staurolite, and the regular arrangement of its carbonaceous inclusions. American Journal of Science, Vol 47, pp 81-89.


Staurolite
USA
New Mexico, San Miguel Co., Cowles, Mora River

Staurolite 1 in. crystal ©



Staurolite
USA,
New Mexico, Taos Co., Picuris District


Staurolite© 2008 Peter Cristofono


Staurolite is known from several localities in the Picuris Range south of Taos. The rocks here belong to the Hondo Group, which are island arc rocks, metamorphosed in the Colorado orogeny some 1.78-1.65 GA. The staurolites are found in the Rinconada formation, which is divided into 6 different members. Staurolite is found in the R1 and R2 schists as crystals up to 3 cm, and in the R6 schist as up to 5 cm crystals. The staurolite is associated with small (up to 3 mm) almandine crystals.

References:

Paul W. Bauer and Keith I. Kelson (2003): Unit Descriptions for Taos Area Geologic Quadrangle Maps (Carson, Taos SW, Ranchos de Taos, Taos, Los Cordovas Quads), New Mexico Geological Survey.

Micheal E. Barret and Caroly E. Kirschner (1979): Depositional systems in the Rinconda Formation (Precambrian), Taos County New Mexico.

Staurolite
USA,
New Mexico, Taos Co., Hondo Canyon District


Staurolite 2.7x2 cm© Jorge M. Alves
Staurolite 19x19 mm© 2005 Ted French

Staurolite & garnet 3.8 cm wide©

Hondo Canyon is probably the most accessible of the staurolite localities near the Picuris Mountains. It lies about 3 miles east of Pilar and is accessible with a high clearance 4-wheel drive vehicle. Staurolite is locally abundant in schists belongin to the R1 of the Rinconada formation. Holdaway and Goodge use R0 on small local patches of schist where staurolite is the dominant mineral (up to 30-50% of the rock) The staurolites are most common as single crystals. X-twins are common with cross-twins being harder to find, and trillings are exceedingly rare. Most specimens have associated almandine (up to 2-3mm). The individual staurolite crystals rarely exceed 3 cm.

The staurolites are mostly worked from placers in the canyon, but may also be recovered from the schist. In 1982, one could purchase a 100 count bag of staurolite crosses, up to 1.5 inches, for $40 - just 40 cents each - but even though the placers are still worked by local collectors, the material is not as abundant as it used to be.

References:

M. J. Holdaway, J. W. Goodge (1990): Rock pressure vs. fluid pressure as a controlling influence on mineral stability: An example from New Mexico, American Mineralogist, Volume 75, pages 1043-1058.

Paul Bauer and Keith Kelson (1998): Preliminary geologic map of the Taos SW quadrangle, Taos County, New Mexico, New Mexico Bureau of Geology and Mineral Resources Open-file Map Series OFGM 12.

Patrick Haynes (2013): Mindat messageboard.


Staurolite
USA,
South Dakota, Pennington Co., Oreville District, US 16 roadside


Staurolite 28 mm crystal© E.L. Clopton
Staurolite 50 mm specimen© E. L. Clopton

Staurolite is found in metamorphic rocks several places in the Black Hills area. The mineral occurs in a 5 to 20 km wide band in an east/west direction north of the Harney Peak granite. Consequently, Roberts and Rapp (1965), in their “Mineralogy of the Black Hills”, conclude that "Staurolite is found in great abundance in many schists in the Black Hills". They list several locations in Pennington and Custer counties, this being just one of them. Maximum crystal size is 2 inches.

The staurolite is found in metamorphic schists that originate from platform and deep marine sediments (1880-2100 Ma), which have later undertgone low-pressure, high-temperature metamorphism accompanying emplacement of the Harney Peak granite.

References:

Willard L. Roberts and George Rapp, Jr. (1965): Mineralogy of the Black Hills, Bulletin 18, South Dakota School of Mines and Technology.

Craig S. Schwandt, James J. Papike, and Charles K. Shearer (1996): Trace element zoning in pelitic garnet of the Black Hills, South Dakota. American Mineralogist, Volume 81, pages 1195-1207.


Staurolite
USA,
Virginia,


Staurolite Largest crystal is 28 mm x 22 mm © BJM


The staurolites from Henry, Patrick, Grayson and Carroll Counties, Virginia are formed by the same events that formed the Appalachians. Staurolite can be found in similar rocks along the entire US east coast. The Appalachians were created following the rifting of the Rodinia supercontinent and subsequent orogenic events, including the Taconian, the Acadian, the Neoacadian and the Alleghanian. This gives a complex melange of island arc and stable shelf metasediments, metavolcanics and intrusive rocks of variable composition and metamorphic grade.

Staurolite-grade metapelites are found in patches along the entire mountain chain, in rocks belonging to different formations. In Virginia, outcrops in several counties carry staurolite, and more frequently sericite pseudomorphs after staurolite. In some rare cases, sillimanite pseudomorphs after staurolite are known, indicating prograde metamorphosis of the staurolite schists.

The sericite pseudomorphs occur in the Fork Mountain schists. These are often fully or partly pseudomorphs after twin crystals, and are the source of the popular “fairy cross” twins. Moore (1936) gives a detailed account on the occurrence of these staurolites:

“The staurolite crystals occur as reddish brown idioblasts, one tenth of an inch up to one and one-half inches in length [Henika (1971) describes crystals up to 7 cm], and are altered wholly or in part to sericite and chlorite. They contain numerous inclusions of small garnets, which weather out giving the appearance of pits in the staurolite crystals.

The staurolites are generally twinned, although not a few occur as simple crystals with usually only a prism and basal pinacoid developed. Occasionallv other crystal forms appear, particularly macro- and brachy- pinacoids and domes. No bipyramids were observed. Penetration twins according to two laws are common, yielding X-shaped and cross-or plus-shaped twins. A careful study of many crystals has shown that 75/s are twinned according to the first law. In this type of twinning, the twin plane 2(232) crosses at angles varying from 35 to 60 degrees. The greater number are nearer the latter figure. Many of them show multiple twinning, a given crystal being penetrated by two or more crystals. Aggre gates containing a number of the X-shaped twins, as well as simple crystals, are of frequent occurrence. Cruciform crystals crossing nearly at right angles make up less than 5/6 of the total number observed

The brown colour observed in crystals on the market is not characteristic of the natural crystal. Many, no doubt, have been artificially coloured. Practically all specimens show numerous pits which have resulted from the dropping out of inclusions. Where these inclusions are still present they are usually garnets. The greenish colour can be traced to the alteration products, chlorite and sericite, as is shown under the microscope.
The alteration to sericite generally begins along fractures and cleavage planes and works outwards, until in some cases' the entire crystal is involved. In many of the intermediate stages a cris-cross pattern results from alteration along intersecting planes.”

Moore’s account illustrates that “fairy crosses” in the trade are rarely natural - not in 1937 and not today. They are often ground into shape (easily done with a sericite pseudomorph), dyed or manufactured from other material. Roberts (1934) gives an account of how this has been done ever since the fairy crosses became popular in the early 20th century.

“The artificial crosses are cut from a talcose schist of a gray color and of a hardness ranging from about 2 1/2 to 3. Thin and narrow band saws fitted on modified grooves of sewing machine pulleys, are used to cut the crosses into rough form; the finishing is done by flat files. The final step is to soak the cross in linseed or some other oil, which gives a dark brown color resembling the color of a natural staurolite when carried in a pocket for some time. Even the compound crosses have been taken seriously by some mineralogists, but the straw which broke the camel's back was that some of the natives produced a staurolite cut after the pattern of a swastika”.

The specimens in the photo above corresponds well with how staurolites and pseudomorphs are made. The fake material presented by Bill Cordua may well have been manufactured in the same manner as described by Roberts, although swastikas are for obvious reasons out of fashion.

Smaller, unaltered, untwinned, prismatic staurolite crystals are found in the Alligator Back Formation.

References:

Joseph K. Roberts (1934): Virginia staurolites as gems, American Mineralogist Vol. 19, pp 549.

Charles H. Moore, Jr. (1937): The staurolite area of Patrick and Henry Counties, Virginia, Vol 22, pp 990.

William S. Henika (1971): Geology of the Basset quadrangle, Virginia, Report of investigations 26, Virginia Division of Mineral Resources.

William S. Henika, James F. Conley, and Palmer C. Sweet (1996): Geology and Mineral Resources of Henry County and the City of Martinsville, Virginia, Publication 137, Virginia Division of Mineral Resources.


Staurolite
USA,
Virginia, Henry Co.


Staurolite 2.0 cm crystal © Maggie Wilson

Several outcrops in Henry Co. have produced similar crystals; see Moore (1937).


Staurolite
USA
Virginia, Patrick Co., Fairy Stone State Park, Patrick Co., Virginia, USA

Staurolite 19 mm crystal ©
Staurolite 3 cm largest crystal ©

These sericite pseudomorphs after staurolite are often ground to improve appearance. The left photo is an example of this.


Staurolite var Lusakite
Zambia
Lusaka Province, Lusaka, Lusakite occurrence


Lusakite 0.7 mm FOV © S. Vrána


Lusakite was found in a rock of gneissic appearance in which it is intimately associated with quartz, kyanite, and magnetite. Parallel to the foliation of the rock are vuggy streaks in which well- developed crystals are found. The average grain size of the mineral is about 2 x 1 x 0.5 mm and individual crystals range from microscopic dimensions to 5 mm long. In hand specimens, the color is black, but minute crystals are deep cobalt-blue by transmitted light. The mineral gives a light blue streak, so that hand specimens of the lusakite-bearing rock often show blue patches due to impact and abrasion.

This quartz-magnetite-lusakite-rock was found on a hillside as a few well-jointed float boulders obviously representing a broken down outcrop and indicating a vein or bed a few inches in thickness and extending possibly for thirty yards along the strike. Associated with these boulders were found larger pieces of a very interesting cordierite-anthophyllite rock, thought to be genetically connected with the lusakite rock.
Staurolite var. lusakite is included in this article because it is one of the very few silicatates with Co as an integral part of the composition. Experiments on synthetic lusakite indicate a solid solution series between the end members staurolite and Co-dominant lusakite.

References:

C. Skerl, F. A. Bannister and A. W. Groves (1934): Lusakite, a Cobalt-Bearing Silicate from Northern Rhodesia. Mineralogical Magazine 23, Vol. pp 598-606.

Lyle V. Phillips & Dana T. Griffen (1986): Staurolite-lusakite series. I. Synthetic Fe-Co staurolites, American Mineralogist, Vol. 7l, pp 1461-1465.

Olav Revheim Sept 2013


Click here to view Best Minerals S and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.



Edited 39 time(s). Last edit at 01/12/2014 01:59PM by Becky Coulson.
avatar Re: Staurolite
August 09, 2013 02:44PM
    
staurolite
USA
New Mexico, Pillar Taos co.



ynot rock'
Tony
Re: Staurolite
August 09, 2013 04:52PM
    
Tony,

Thank you for bringing this locality to my attention, I will check it out when I am back working on the article. Any information how good the staurolite from here gets will be appreciated. The photos you have attached are unfortunately too blurry to be added to the article.

smiling smiley

Olav
Re: Staurolite
August 09, 2013 05:17PM
    
You also missed this one [www.mindat.org]
avatar Re: Staurolite
August 09, 2013 05:46PM
    
Picurus - Staurolites are between 1 and 4cm in size. 60 degree twins are dominant, 90 degree are common, stellate trillings are uncommon.

Virginia
Carroll and Grayson counties - single crystsls to 2-10 by 40cm
Henry County - single crystals to 13x25x50cm

Fannin county Ga.- crystals to 5cm
Re: Staurolite
August 09, 2013 05:50PM
    
Thanks Reiner and David smiling smiley



Edited 1 time(s). Last edit at 08/09/2013 05:54PM by Olav Revheim.
Re: Staurolite
August 09, 2013 06:54PM
    
Hondo Canyon in Taos County also produces good Staurolite crystals. See [www.mindat.org]. John S.
Re: Staurolite
August 09, 2013 07:03PM
    
Thanks John

smiling smiley

Olav
Re: Staurolite
August 09, 2013 08:41PM
see also: [www.mindat.org] for the Co-bearing variety lusakite
Re: Staurolite
August 09, 2013 08:52PM
I think the sample on the right in the photos from "Fairy Stone Park, Virginia" does not look real. I've seen these for sale and not only is their color off, but their density is suspiciously low, and they often have small air bubbles that seem unlikely to me to form in a metamorphic mineral embedded in schist. Are these faked? Reconstituted in some way? Anyone else have any thoughts on these particular items that are sold and marked "staurolite"?
avatar Re: Staurolite
August 09, 2013 10:16PM
Tony, those are good specimens and I think we could use them in the article, but they would need a better picture in focus or of higher resolution and they would need to be uploaded to mindat's gallery before we could use them. I especially like the one with the garnet.

Rock Currier
Crystals not pistols.
avatar Re: Staurolite
August 12, 2013 04:25PM
    
Olav,
thanks. the crystals that i found there have a nice luster, but the seface is somewhat uneven. there were 90 degree "crosses" and single crystals found there but most (98%) were the 60 degree angle twins. the largest were about 5.3cm in length x 4cm wide. the thickest were 2cm across. all had the dark reddish brown couler.
hope this helps you.here are two pics of a single crystal from the site.




ynot rock
Tony
Re: Staurolite
August 12, 2013 04:52PM
    
Thank you Tony

smiling smiley

Olav
avatar Re: Staurolite
August 13, 2013 01:40PM
    
Olav,
Rock Currier questioned the name that i gave for this location.so i looked it up and the site name that i have calls it Pilar, Taos co. New Mexico, USA. the site is northeast of the hedalgo canyon area, about two miles north of the town and east of sate hghway 68.

ynot rock
Tony
avatar Re: Staurolite
August 13, 2013 04:42PM
Hello,
Wonderful article! I don't know if Blanchard dam, Royalton, Morrison Co., Minnesota, USA is significant enough to mention on a "best of" post, but the locality has yielded a few nice pieces that I found:



Re: Staurolite
August 13, 2013 06:56PM
Pearl Lake Hill a/k/a Mink Pond in Lisbon, NH has produced numerous well formed crystals and crosses, some of which can be seen on Mindat!
Re: Staurolite
August 14, 2013 06:05AM
    
Gents,

Thank you very much. I will add these localities to the article.

Thanks

Olav
Re: Staurolite
August 30, 2013 03:28AM
Here's a photo I took of a questionable "starurolite" mixed with some self-collected real staurolite collected from the Royalton area in Minnesota.

Re: Staurolite
August 30, 2013 05:53AM
    
Bill,

Thank you very much!!

Olav
Re: Staurolite
September 11, 2013 04:03PM
Olav, the best minerals/staurolite article has really grown and is very interesting. I was not aware that most of the Patrick County, VA twins are sericite or sericite/chlorite pseudomorphs. I guess those minerals need to be added to the locality and most of the specimens (like mine) need to be relabelled.
(ps - I promise not to bring up the diagonal striations again.)
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