Riebeckite-series

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The Riebeckite series minerals are minerals in the amphibole group, see Amphibole Group main article for an overview of the group. The series contains the following minerals:

Riebeckite
Na₂ (Fe2+₃ Fe3+₂ ) Si₈ O₂₂(OH)₂

Magnesioriebeckite
Na₂ (Mg3Fe3+₂ ) Si₈ O₂₂(OH)₂



The riebeckite-series minerals belongs to the Sodic-Amphibole subgroup, characterized by having Na₂ in the B position of the amphibole molecule. There is a continuous series between riebeckite and magnesio-ribeckite, and also between riebeckite and other amphiboles. The series formed involving a riebeckite component is largely dependant of the geological environment. Although riebeckite is a very common mineral ( riebeckite is listed from 314 localities in Mindat and magnesioriebeckite 70), also in large crystals, good specimens are few and far between.

Riebeckite ( with Fe/Mg>>1) is a common mineral in alkaline granites and syenites. It occurs as a rock forming mineral in these rocks, and large crystals ( up to and exceeding 75cm in maximum length) can be found embedded in pegmatites belonging to riebeckite containing granites. Riebeckite can also be found as free standing crystals in cavities in these granites, often then in the form of asbestiform fibres, crocidolite. This does not necessarily form attractive specimens.

In some of these granites, riebeckite can have a significant F content, and analysis of F dominant riebeckite has been published, thus justifying fluororiebeckite as a "named" amphibole species.

In alkaline granites and syenites, a continuous series exist between arfvedsonite and the riebeckite, and the general rule of thumb is that riebeckite is found in the more silica rich alkaline rocks, although this rule is not without exceptions. Riebeckite is also found in metamorphic rocks where it forms a continuous series towards glaucophane.

Riebeckite is stable in lower pressure and temperature environments than other amphiboles and the asbestiform variety crocidolite can be found in sedimentary banded iron formations (BIF's). The crocidolite can be found as in veins and bands in these rocks, although rarely exceeding 10 cm fibre length. In some of these environments, the rocks has undergone only low grade metamorphosis, and it has been suggested that riebeckite can form at temperatures down towards 100 deg C.

The riebeckite Fe/Mg ratio is normally lower in metamorphic rocks, and the rarer magnesioriebeckite can be found in some of these metamorphic environments.

For most of the 20th century, riebeckite asbestos ( ble asbestos, crocidolite) was mined in large mining operations in Australia, south Africa and other places, and the total production can be counted in millions of tons. This mining has been stopped due to the severe negative health effects of asbestos.


Riebeckite
Australia
Western Australia, Pilbara Region, Hamersley Ranges (Hammersley Ranges), Wittenoom (Wittenoom Gorge; "Wittenoon Gorge")



Wittenoom is a ghost town in the Hamersley Range in the Pilbara region of Western Australia. It’s growth and fall is largely linked to the production of riebeckite asbestos from the 1930-ties to 1966.During its heydays in the 1950-ties, Wittenoom was the largest town of Pilbara..

A total of 364 tons ( Wikipedia) asbestos was produced. Riebeckite was mined from thin asbestos bands in a banded iron formation (BIF). There are a total of 17 BIF horizons interbedded with shales in the 2,6Ga Dales Gorge Member of the Brockman Iron Formation of the Hamersley Group of metamorphic rocks. Riebeckite occurs in 0,2-15 cm thick bands formed as as fracture fillings essentially parallel with the sedimentary banding, in particular the lowermosts bands. The riebeckite fibers of the wide bands grow perpendicular to the bedding plane.

Riebeckite is often bounded by magnetite mesobands (1-5 mm thick), so called magnetite skins. Riebeckite is associated with magnetite, quartz, pyrite, and rarely ankerite and siderite. Riebeckite are still abundant at the mining sites and as roadfill (!), but it is not permitted to remove any material from the area, as it today is part of the Karijini National Park

Literature:

Miyano, Tikashi and Klein, Cornelius (1983): Conditions of riebeckite formation in the iron-formation of the Dales Gorge Member, Hamersley Group, Western Australia, American Mineralogist, Volume 68, pages 517-529,

Powell, C.McA. and Horwitz R.C.(1994): Late Archaean and early Proterozoic tectonics and basin formation of the Hamersly ranges, Geological Society of Australia, Excursion guidebook No 4

Wikipedia


Magnesioriebeckite
Bolivia
Cochabamba Department




Magnesioriebeckite
Bolivia
Cochabamba Department, Chapare Province, Alto Chapare District

Magnesioriebeckite 80mm tall specimen	© Joseph A. Freilich

Magnesioriebeckite in the upper part of the Alto Chapare District is found in Cambrian sediments of the Limbo formation. This formation consist of a sequence of compact anhydrite, magnesite, dark shales and calcareous siitstones. Metasomatic influx of Sodium and Magnesium is responsible for forming magnesioriebeckite as well as magnesite and talc. (The source of the Na and Mg was actually the underlying evaporites of the Locotal Breccia formation. - Alfredo Petrov)

The magnesioriebeckite was mined for asbestos in the 1930-ties and 1940-ties, and most of the research on this occurance originates from this period or at latest in the 1950-ties when asbestos still had a economic potential. This was before the general acceptance of the theory of plate tectonics, and the understanding of its significance for rock forming mechanisms was not as matured as today. Therefore the regional geological processes involved in the formation of an amphibole in an unusual environment are poorly described, but it has been proposed that ultrabasic magmatism in beginning of the Paleozoic may be the source of the Na and Mg required to form magnesioriebeckite. (The mineralogy of this district was poorly understood when these reports were written in the 1940s and 50s. In reality there was no igneous activity at all; the Na and Mg were derived from older evaporites, now represented by the slightly metamorphosed saltdome caprocks of the Locotal Breccia. Magnesioriebeckite can be found in small quantities within the meta-evaporites of the Locotal Breccia itself, for example together with magnesite or povondraite on the outer crust of altered clasts (xenoliths), and as parallel inclusions giving chatoyancy to the very rare blue "catseye" danburite gems. - Alfredo Petrov)

It has been estimated that overall reserves of 30,000 tons of magnesioriebeckite are present in these rocks, but not a lot has been produced. There are many open pits and small mines spread over an 8 km long belt. The most famous, and the one with the most extensive underground workings, was the San Francisco mine, now completely buried under the rainforest. Currently (1990s to 2012) the most active is the open pit Filadelfia mine.

The magnesioriebeckite ”are composed of crudely rectangular fibrous bundles up to 1 in. across, the bundles being oriented in all directions with respect to each other.” (Hodgson 1965). Fibres reached up to 1 metre long!

Literature:
Hodgson A.A. (1965), The thermal decomposition of miscellaneous crocidolites, Mineral. Mag.Vol 35,291-305.

Little, Arthur D. (1970): Surveys of opportunities for Bolivian industry, Volume III


Magnesioriebeckite
Bolivia
Cochabamba Department, Chapare Province, Alto Chapare District, Cristalmayu subdistrict, Cristalmayu, Cristalmayu valley, Filadelfia mine




Riebeckite
Canada
Québec, Montérégie, Rouville RCM, Mont Saint-Hilaire, Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire)

Riebeckite FOV 6,7mm

Riebeckite FOV 7,1mm

The Poudrette Quarry of Mont Saint-Hilaire is well known by mineralogists and collectors all over the world due to the large number of minerals identified there. Mindat lists (April 2012) list 391 minerals and 57 type minerals. 11 amphiboles are known from the quarry, riebeckite being one of them.

The Poudrette Quarry lies in the “East Hill Rock Suite” within the Mont Hilaire intrusiuon, which in turn is is a member of the Early Cretaceous Monteregian Hill, a group that includes ten separate alkaline intrusions arranged in a linear array extending approximately 235 km from Oka just west of Montrral to the Qurbec-Maine border in the east. The East Hill Suite consist predominantly of nepheline syenite and sodalite syenite, awide variety of rock types is found in the quarry and reflects complex conditionsunder which crystallization took place. This variety of rock types includes pegmatites, marble xenoliths, sodalite syenite, nepheline syenite, hornfels,igneous breccias and sodalite syenite xenoliths.

Riebeckite is not a common mineral at the Poudrette quarry, as it is found only in hornfels xenoliths, and most likely also in marble xenoliths, although I have not found any analysis confirming the occurance of riebeckites in the marble xenolithes. In these rocks, however, riebeckite can be quite abundant as star shaped, light blue fans and fibrous aggregates up to 6cm in diametre. This mode of occurance is supposedly diagnostic for riebeckite at the locality.

Literature:

Mandarino Joseph Anthony and Anderson Violet (1989), Monteregian Treasures: The Minerals of Mont Saint-Hilaire, Quebec

Lalonde A.E and Rancourt D.G and Chao G.Y.(1996), Fe-bearing trioctahedral micas from Mont Saint-Hilaire, Quebec, Canada, Mineralogical Magazine, Vol. 60, pp. 447~160

Marc Favre, Mont Saint Hilaire : Micro-Mineral Paradise, webpage


Riebeckite
Kenya
Machalcos District, Sultan Hamud, Masokani Hill,

The following quote deserves it’s place in this article:

” Fine specimens of striated, bladed prismatic and acieular riebeckite,sometimes radiating or platy, from the western flank of Masokani Hill, 9 miles NNW. of Sultan Hamud, Machakos District, Kenya, were acquired by the British Museum (Natural History) in 1944 (B.M. 1944,105-9, 111) by exchange with Dr. C. Stansfield Hitchen, then Senior Government Geologist in Kenya. The riebeckite crystals, which are up to 6 cm in length, appear to have grown in a small vug or pccket,associated with quartz and, to a lesser extent, platy ilmenite and goethite pseudomorphing chalybite. Crocidolite (asbestiform riebeckite) has also been found. In one specimen (B.M. 1944,107) the riebeckite and quartz grow out of a highly weathered granitic rock, largely consisting of microcline microperthite, with some quartz and riebeckite.

In 1946, a magnificent specimen of riebeckite prisms intergrown with and included in large quartz crystals, of total weight 97 lb (fig. 1), was presented to the Museum by Major H. W. J. Lambert, who relates how he found the specimen in 1940 at a locality some 10 miles south of Sultan Hamud railway station, had it carried on a pole and canvas
stretcher to the railway line, waved down the train, and conveyed it safely to Nairobi, where it was exhibited at the Coryndon Museum. The largest riebeckite crystals on this specimen are 18 cm long and 1-6 cm across; the acicular crystals included within the quartz are randomly oriented, in the futile habit. Dr. Hitchin saw the specimen and considered that it was almost certain to have originated at Masokani Hill and been taken to the second locality by the local inhabitants.”

Literature

W. CAMPBELL SMITH, M. H. HEY, D. R. C. KEMPE (1968): Riebeckite from near Sultan Hamud, Machalcos
District, Kenya


Riebeckite
Madagascar
Antsiranana Province, Diana (Northern) Region, Ambanja District, Ampasindava Peninsula, Ampasibitika



The Ampasindava peninsula contains several igneous intrusives of variable compositions, including syenites, gabbros and granites. The landscape is very steep and covered by dense rain forest, making petrologic and mineralogic mapping difficult. The prime source of information is (according to Woolley) still Lacroix’ (1922-23)three volume “Mineralogie de Madagascar”. The Ampasibitika ( Ambohimirahavavy) is a 18km long mixed intrusive and extrusive complex, where the intrusive rocks are predominantly riebeckite bearing granites grading to syenites. In pegmatites, riebeckite can form well-formed crystals up to 20cm long, embedded in feldspar. Due to the difficult access and the difficulty in retrieving good specimens from massive rocks, not many riebeckite specimens from here find its way into collections.

Literature:

Alan R. Woolley(2001): Alkaline Rocks and Carbonbatites of the World, Part III. Africa, The Geological Society of London


Riebeckite
Malawi
Zomba District, Mount Malosa

Riebeckite 7 cm specimen	© Russell G. Rizzo

Riebeckite 4 cm specimen	©

The early Cretaceous Chilwa Alkaline Province has an exceptional range of lithologies from carbonatite to granite. It lies at the southern end of the East African rift and is unique for it’s essential intrusive character. The largest and most recent (ca 113Ma) intrusions are those that consist of syenite and peralkaline granite. The Chinduzi-Chikala (nepheline) syenites are older (up to 130Ma)

The well crystalized minerals from the area comes from the Zomba-Malosa intrusion and the Chinduzi-Chikala mountain range. Mount Zomba consists of a central plug of syenite, an inner ring of quartz microsyenite and an outer ring of peralkaline granite. Mount Malosa the consist of a heterogenous mix of quartz-syenites and granites. These two mountains are divided by a deep rift valley. Numerous amphiboles has been identified from the Zomba-Malosa intrusion, and the “amphiboles cover an exceptionally extensive range of species including calcic, sodic-calcic and alkali types. They define distinct Zomba and Malosa trends of Mg depletion and alkali enrichment and increase in Fe3+: Fe2 ratios”(Wolley and Jones, 1992).

The Chinduzi-Chikala mountain range consist predominantly of of syenite, which gradually becomes more silica undersaturated from east(syenite) to west (nepheline syenite)

The attractive mineral specimens originates from pegmatites related to these rocks, and two important types of pegmatites are present in the area:. “ In the Chinduzi-Chikala range of mountains, nepheline-syenite pegmatites occur. These contain large well developed aegirine crystals “….. up to 5 by 2.5 cm in size…..” as reported by Bloomfield (1965). In contrast, granitic pegmatites are found in the Zomba Mountain and Malosa Mountain. The northwestern fault scarp in particular has an abundance of these pegmatites and it is from these deposits that the best specimens have been collected. To the south, the Zomba section of the complex has far fewer pegmatites.” Cairncross(2004).

In most mineralogy litereature, the primary (and sometimes also the secondary) amphibole is named arfvedsonite. Arfvedsonite is without doubt a common mineral in many of the pegmatites, and well formed crystals exceeding 10 cm are known. Identification all the well formed pegmatitic amphiboles as arfvedsonite does not take into account the varying lithology and the wide variation of amphiboles present in these rocks. Typically, riebeckite will be the primary amphibole in silica saturated alkaline rocks such as the granites and quartz syenites of the Zomba-Malosa intrusive and arfvedsonite would be more typical for the silica underaturated rocks of the Chinduzi-Chikala range (although this is sometimes partly replaced by secondary riebeckite). However, as Wolley and Jones points out, the range of amphiboles present in these rocks are “exceptional”, and it is likely that a variety of amphibole species also will be available from the pegmatites.

Literature:

Peter E J Pitfield(2009): Mineral Potential of Malawi 1- Mineral deposits associated with alkaline magmatism (rare earth metals, coltan metals, nuclear metals, phosphate, etc.), Ministry of Energy and Mines, Republic of Malawi

Soman, Aneesh and Geisler, Thorsten and Tomaschek , Frank and Berndt, Jasperand Putnis, Andrew1(2008), Hydrothermal Alteration of an Alkali Pegmatite from Zomba-Malosa (Malawi)

Woolley A.R. and Jones G.C.(1992), The alkaline/peralkaline syenite-granite complex of Zomba-Malosa, Malawi: mafic mineralogy and genesis-abstract, Journal of African Earth Sciences (and the Middle East) Volume 14, Issue 1, Pages 1–12

Cairncross, Bruce (2004), Aegirine and Associated Minerals from Mount Malosa, Malawi, South African Lapidary Magazine Vol . 3 6 . 2


Riebeckite
Pakistan
Khyber Pakhtunkhwa (North-West Frontier Province), Peshawar, Hameed Abad Kafoor Dheri, Zagi Mountain (Zegi Mountain; "Shinwaro")

Riebeckite 3,1 cm specimen	© Rob Lavinsky

Riebeckite is the dominant dark mineral in the Warsak alkaline granites, which is a part of the Peshawar plain alkaline igneous province (PAIP). Occationaly riebeckite included quartz crystals re flund in vugs in these granites.


Riebeckite
Portugal
Portalegre District, Alter do Chão, Alter Pedroso

Riebeckite 10 cm specimen	© Rui Nunes 2009

Alto Pedroso is a small hill consisting of a metamorphosed alkaline syenite ( syenitic orthogneiss) surrounded by predominantly granitic gneiss and metagabbro. The alkaline rocks is contained within the hill itself, covering a surface area roughly 2x1 km. The syenitic orthogneiss carries riebeckite and aegerine as the dark minerals together with albite microcline and occasionally quartz and zircon. The rock itself is rather fine grained, and of more interest for petrologists than mineral collectors. Larger crystals can be found in alkaline pegmatites. Lacroix (1916) investigated samples in the collection of the Sociedade Geológica de Portugal, and he describes riebeckite crystals up to 40 cm. Also large zircones are known from these pegmatites.

At the turn of the 20th century, scientists considered the origin of this intrusion a bit mysterious, but recent papers see this intrusion in conjunction with other intrusions of similar age ( 482Ma).

Literature:

SERRALHEIRO, António(1957), Esboço geológico da região de Alter Pedroso: Boletim da Sociedade Geológica de Portugal, Vol. XII, fasc. III, p. 3-12.

M. A. Lacroix (1916): Les syenites a riebeckite d'Alter Pedroso {Portugal), leurs forms mesocrates (lusitanites)et leur transiformation en leptynites et en gneiss. DES SEANCES DE L'ACADEMIE DES SCIENCES, PARIS

UMBERTO G. CORDANI, ALLEN P. NUTMAN, ANTONIO S. ANDRADE,JOSÉ F. SANTOS, MARIA DO ROSÁRIO AZEVEDO, MARIA HELENA MENDES and MANUEL S. PINTO (2006):New U-Pb SHRIMP zircon ages for pre-variscan orthogneisses from Portugal and their bearing on the evolution of the Ossa-Morena Tectonic Zone, Anais da Academia Brasileira de Ciências 78(1): 133-149


Magnesioriebeckite-Riebeckite Series (Var: Crocidolite)
South Africa
Northern Cape Province




Magnesioriebeckite-Riebeckite Series (Var: Crocidolite)
South Africa
Northern Cape Province, Griqualand

Crocidolite is 5.2 x 3.2 x 2.9cm specimen	© Jasun McAvoy

All the South African localities are are described in one text entry, as the occurence of the mineral, the geology and the mining history is common for all localities. The first account of riebeckite asbestos (crocodolite) from South Africa dates back to 1803 when the German geologist H. Lichtenstein reported the occurrence of “Blau Eisenstein” near Prieska in the Orange river valley. Mining of asbestos did not commence until 1893. From the start, only primitive mining by “independent groups of contractors” took place. Asbestos was retrieved from the ground by pick and shovel before it was hand sorted and sold to a larger mining corporation. In 1914 the production using these methods reached 1000 tons/yr, in 1949, the production had increased 10000 tons/yr.

Industrial production started in the 1950-ties due a huge demand for asbestos from Europe and the USA and by 1962 the annual production exceed 100.000 tons. The production continued to increase until it peaked in 1977 at 379,000 tons, after which the demand decreased rapidly and by 1992, all mining for riebeckite asbestos was shut down. For a number of reasons, it is hard not to get a bit upset when reading contemporary accounts from the production.

Crocodolite was originally mined from countless small pits and outcrops over a large area, following a geologic horizon over 240 miles from south of Prieska to north of Tsenin in Kuruman. Hanekom(1966) lists 143 crocodolite occurrences, and also provides details of many of them. As the mining became more industrialized, the mining operations were consolidated, and in late 1970-ties, only 10 large mines were in operation. The mining operations had significant negative impact on both the environment and people’s health.

Dr. C. A. Sleggs describes his first visit to Kuruman in 1948 (prior to the onset of large scale industrial mining) like this: “When I first saw it, the land was blue for miles around the asbestos settlements. The mills indiscriminately spewed blue dust clouds over the countryside and whenever the wind rose, a blue haze hovered over the dumps”. Research has shown that crocodolite dust poses an even larger health risk than anthophyllite and serpentine asbestos. Despite the well documented negative health effects, the total impact on the population is poorly known until the 1980-ties when South Africa had the highest rate of asbestous related illness in the world. Still today remains from the mining industry causes environmental and health issues and there are hundreds of un-reclaimed mines in South Africa that have made large areas of the northern Cape permanently hazardous. A recent study by Kielkowski et al (2011) show that the mesothelioma mortality rates far lower than expected, and lower than large asbestos consuming nations like UK and the Netherlands. The conclusions drawn from this study are rather depressing though; the authors believe the reduction in mesothelioma deaths is largely due to AIDS killing people before mesothelioma can develop.

The crocodolite fibres, sought after and produced at so high human and environmental cost was found in Banded Iron Formations (BIF's) in what is termed the Cape Belt, consisting of an about 3000ft thick series of magnetic jaspers and siliceous ironstones with very subordinate sandstones, limestones and cherts. These beds form the lowest member of the Griquatown Series which in turn represents the uppermost of the three subdivisions of the Transvaal System in Griqualand West. The riebeckite bearing BIF’s of the Griquatown Series has a typical bulk chemistry compared to other large-scale iron-formations of the Precambrian, which all formed in chemically very similar environments by biochemical and hydrothermal processes.

The crocodolite itself occurs as a blue fibrous seams in the host rock. These seems may be mm-thick, but may also reach widths exceeding 10 cm, and seams wider than 3mm was considered exploitable. The fibers are normally perpendicular to the bedding of the rock, always with a magnetite rim, sometimes with a thin layer of chert between the crocodolite and the magnetite, and sometimes the crocodolite is interbedded with thin magnetite beds. When exposed in outcrops, the crocodolite seams is oxidized to a ochre color, eventually decomposing to a yellow crumbling powder ( "limonite").

These crocodolite seams constitutes a significant portion of up to 500ft thick horizons of the rocks in multiple sequenzes. Hanekom (1965) gives a detailed account on the rocks of the crocodolite bearing horizons in the Griqualand West sequence.

South African tiger's-eye (golden) and hawk's-eye(blue) come from an area near Griquatown and Niekerkshoop, Northern Cape Province. These are silicified crocodolites that is ( tiger’s eye), or is not (Hawk’s eye) altered to goethite. It has generally been believed that these lapidary stones are prime examples of pseudomorphs of quartz and goethite after riebeckite. Heaney and Fisher (2003) propose, based on crystallographic and optical investigations, an alternative theory. They consider the origin of tiger’s eye and hawk’s eye to becaused by a discontinuous crack-seal mechanisms: “Episodic cracking along the vein margins separated quartz-rich vein material from the host-rock walls, and crocidolite fibers grew by syntaxial crystallization on preexisting crocidolite grains in the host rock. These crocidolite overgrowths then were encapsulated by columnar quartz that grew antitaxially off the opposing vein wall. The vein quartz crystals and their crocidolite inclusions separated from the host-rock wall during a subsequent cracking event. Thus, after each
fracture episode, quartz encapsulation followed crocidolite overgrowth, and the cycle was repeated to create veins with dimensions of millimeters to typically a few centimeters in thickness.”

This theory has been disputed based on field observations, stating that tiger’s eye and hawk’s eye occur only where the BIF’s crosscut the Mesozoic African land surface, thus creating an altered 2–4-m-thick zone of massive silicification and goethitization, which is the only environment, although widespread in this region, where tiger’s eye and hawk’s eye can be found

Literature:
Uwe E. Horstmann,Ingo W. Hälbich(1995): Chemical composition of banded iron-formations of the Griqualand West Sequence, Northern Cape Province, South Africa, in comparison with other Precambrian iron formations, Precambrian Research, Volume 72, Issues 1–2, Pages 109–145

Harding, C.J., 2004. Origin of the Zeekoebaart and Nauga East high-grade iron ore deposits, Northern Cape Province, South Africa. Master’s thesis, University of Johannesburg,South Africa.

HANEKOM, H.J., 1966. The crocidolite deposits of the northern Cape Province: DSc. thesis, Univ. Pretoria (unpubl.).

G. K. Sluis-Cremer(1965), ASBESTOSIS IN SOUTH AFRICA - CERTAIN GEOGRAPHICAL AND ENVIRONMENTAL
CONSIDERATIONS, Annals of the New York Academy of Sciences Volume 132, Issue 1

JOCK MCCULLOCH (2003), Asbestos Mining in Southern Africa, 1893–2002 International Journal of Occupational and Environmental Health, VOL 9/NO 3,

D Kielkowski,G Nelson, B Bello, S Kgalamono, J I Phillips (2011): Trends in mesothelioma mortality rates in South
Africa: 1995- 2007, Occupational and Environmental Medicine, vol 68 pages 547-549.

Peter J. Heaney and Donald M. Fisher (2003): New interpretation of the origin of tiger's-eye, Geology volume 31 pages 323-326

Jens Gutzmer,Nicolas J. Beukes, Bruce Cairncross(2004): New interpretation of the origin of tiger's-eye: Comment and Reply, Geology, vol. 32, no. 1,

Martin A. Peacock(1928), THE NATURE AND ORIGIN OF THE AMPHIBOLE ASBESTOS OF SOUTH AFRICA, The American Mineralogist Vol 13 no 7

J. GUTZMER, BENNY C. CHISONGA, NICOLAS J. BEUKES, JOYDIP MUKHOPADHYAY (2008), The Geochemistry of Banded Iron Formation-Hosted High-Grade Hematite-Martite Iron Ores, Society of Economic Geologists
SEG Reviews vol. 15, p. 157–183


Magnesioriebeckite-Riebeckite Series (Var: Crocidolite)
South Africa
Northern Cape Province, Kalahari manganese fields, Kuruman



Several asbestos mines operated near Kuruman. An asbestos mill was operational in the centre of the town for many years.


Magnesioriebeckite-Riebeckite Series (Var: Crocidolite)
South Africa
Northern Cape Province, Namaqualand, Prieska District



The city of Koegas in the Prieska district has been a major producer of blue asbestos from 1893 to 1979.


Magnesioriebeckite-Riebeckite Series (Var: Crocidolite)
South Africa
Northwest Province, Vryburg, Pomfret Mine



The Pomfret mine was one of the main producers of crocidolite asbestos from the 1926 to 1986/7


Riebeckite
USA
Colorado, El Paso Co., Cheyenne District (St. Peters Dome District) , St Peters Dome

Riebeckite 9,7 cm specimen	© David J. Eicher

The earliest accounts of the area record the discovery of unusual minerals in pegmatites of the St. Peters Dome district, which attracted attention of mineralogists as early as earlv as 1877 (Koenig, 1877). Bastnaesite and fluocerite were among the earliest found (Allen and Comstock, 1880). Later the fluorides cryolite, pachnolite and prosopite were identified and analyzed from these pegmatites (Cross and Hillebrand 1883, 1885; Hillebrand, 1899 ( Crossa and Hillebrand).

Dikes of pegmatite are widely distributed throughout the area of granite, especially northeast of St. Peters Dome and along the valley of South Cheyenne Creek. Approximately 150 pegmatite dikes were examined in this period, dividing the pegmatites in two principal types, a calc-alkalic
Granitic (genetically related to the Pike Peak granite) and an alkalic granitic type (related to the Mount Rosa Granite). Most are of the latter variety, and it is this variety that carries riebeckite crystals. Gross and Heinrich(1965-66) divides the alkali pegmatites into three subcategories:
1 pegmatites that are well within the Mount Rosa granite sheet. These are small, lenticular segregations or small injected pegmatites, that range in thickness from one foot to 15 feet, and are exposed in outcrops from a few feet to 50 feet long. Riebeckite crystals, although several cm long, are smaller than those found in the other two groups

2 Pegmatites external to, but still in the vicinity of the Mount Rosa granite. These are injected bodies, which are larger than the interior type but are usuallv less than 6 feet thick and show surface exposures commonly less than 20 feet long. These exterior dikes have coarser grained textures than their interior relatives, and their contacts with the Pikes Peak granite are sharp.

3 Pegmatites found several miles from the Mount Rosa granite. These are the largest dikes of the area; however, they are few in number. Most are
6 to 8 feet thick and are irregular, Ienticular bodies with sharp contacts with the granites. They are poorly zoned, but mineralogically very complex. In these exterior pegmatites, riebeckite may form crystals up to 15 cm by 75 cm.

Literature:

George I. Finley (1916) Description of the Colorado Springs Triangle, US. Geol. Survey Geol. Atlas, Folio

Eugene. B. Gross and E. Wm. Heinrich (1966), PETROLOGY AND MINERALOGY OF THE MOUNT ROSA AREA, EL PASO AND TELLER COUNTIES, COLORADO.II. Pegmatites THE AMERICAN MINERALOGIST, VOL. 5 1

Eugene. B. Gross and E. Wm. Heinrich (1965), PETROLOGY AND MINERALOGY OF THE MOUNT ROSA AREA, EL PASO AND TELLER COUNTIES, COLORADO.II. The Granites THE AMERICAN MINERALOGIST, VOL. 5 0


Riebeckite
USA
Colorado, El Paso Co., Mount Rosa, Rosa No. 1 trench



The Mount Rosa granite is an alkalic riebeckite granite that can be found in small bodies in a
Four by one mile area. The largest body is two by one mile and between 12 to 150 ft thick. The 1040Ma granite is considered to belong to the same magmatic event as the larger Pike’s Peak granite, into which the Mont Rosa granite has intruded. The granite itself consists of microcline and quartz, containing up to 20% riebeckite as the dominant dark mineral. The main granite bodies are relatively fine grained, with the average size blue-black riebeckite blades no more than fractions of a mm thick. The grain size is however variable, and giant crystals can be found in pegmatites associated with the Mount Rosa granite.

George I. Finley (1916) Description of the Colorado Springs Triangle, US. Geol. Survey Geol. Atlas, Folio

Eugene. B. Gross and E. Wm. Heinrich (1966), PETROLOGY AND MINERALOGY OF THE MOUNT ROSA AREA, EL PASO AND TELLER COUNTIES, COLORADO.II. Pegmatites THE AMERICAN MINERALOGIST, VOL. 5 1

Eugene. B. Gross and E. Wm. Heinrich (1965), PETROLOGY AND MINERALOGY OF THE MOUNT ROSA AREA, EL PASO AND TELLER COUNTIES, COLORADO.II. The Granites THE AMERICAN MINERALOGIST, VOL. 5 0


Riebeckite
USA
Colorado, El Paso Co., Stove Mountain (Cookstove Mountain)




Riebeckite
USA
Massachusetts , Essex Co. , Gloucester, Blackburn Circle locality

Riebeckite 2,5mmFOV	© 2009 Peter Cristofono

The Blackburn circle locality was a temporary exposure of boulders and outcrops of the alkali Cape Ann granite. This granite is the largest of a series of late ordovician (+/- 450MA) alkaline intrusives belonging to the Avalone terrane. The granite consists predominantly of medium-grained perthitic alkali feldspar (60 to 65%), quartz (25 to 35%), and less than 10% of the mafic minerals ferrobiotite, ferrohastingsite, and riebeckite with traces of fayalitic olivine and aegirine.

The dominant amphibole in this granite is ferrohastingsite, but in parts of the granite, the amphibole is riebeckite. Thankfully, the two amphiboles can be distinguished based on the color, ribeckite being bluish black and ferrohastingsite greenish black. Riebeckite specimens can be found both as free-standing acicular crystals in miarolitic cavities, star formed groups embedded in the granite, and larger iundividual crystals in pegmatites related to this granite. I am uncertain whether riebeckite bearing pegmatites occured at this specific locality.

Literature:

Rudolph Hon, J. Christopher Hepburn,Jo Laird (2007) Siluro-Devonian igneous rocks of the easternmost three terranes in southeastern New England: examples from NE Massachusetts and SE New Hampshire: Field Trip F4, p. 23-43, in Thompson, P.J., editor, Guidebook to Field Trips in New Hampshire and Adjacent Maine and Massachusetts, Geological Society of America, Northeastern Section, field trip guidebook for the 42nd annual meeting, Durham, NH.

Paul C. Lyons (1972): SIGNIFICANCE OF RIEBECKITE AND FERROHASTINGSITE IN MICROPERTHITE GRANITES, American Mineralogist Vol. 57, pp. 1404-1412 (1972\


Riebeckite (Var: Crocidolite)
USA
Massachusetts , Norfolk Co , Quincy, Granite Rail Quarry (Granite Railway Quarry)



The granite rail quarry is one of many granite quarries near Quincy. Starting in 1826, the Quincy granite has been extensively quarried for use as a building stone. It's popularity peaked in the late 19th century, and the combination of relatively inexpensive steel and concrete building materials, a growing awareness of the health impact of granite dust and higher wages caused a downturn in the Quincy granite industry in the early 20th century, with the last quarry to shut down in the 1960-ties.

The extensive quarrying provided good opportunities for mineralogists and collectors alike, and in particular Warren and Palache (1911) gives a detailed account of the occurence of riebeckite in these quarries, the following quote may serve as a good example:

" The riebeckite forms elongate crystals ranging in size from small grains up to large and very conspicuous crystals, 1 to 2 cm. in diameter and 5 to even 15 cm. in length. The larger crystals are more abundant towards the center and may extend out into the quartz center. Although indented by the feldspar and often including grains of it, the riebeckite, especially
in the larger crystals, shows a tendency to develop a crystal crosssection made up of the forms 110 and 010. Terminal planes are wholly wanting. Without exception the riebeckite is intergrown with aegirite. Commonly in parallel position, though again without definite orientation (c axis in common), the aegirite may occur quite at random in the body of the riebeckite, but it is most abundant about the outside, particularly on the ends, forming an almost or quite continuous shell about the riebeckite. Indeed the ends of the riebeckite crystals are usually continued as a solid mass of aegirite. "

In addition to crystals embedded in the granite and it's pegmatite, riebeckite in the form of crocidolite was common in pockets in the quarries. Warren and Palache gives a detailed account of the "central pocket" discovered in the Fallon quarry. The descriptions starts like this:

" The contents of the large central cavity were most unusual in character and consisted essentially of : quartz crystals
of all sizes from exceedingly minute individuals up to great crystals, 10 cm. thick and 30 cm. long ; rock fragments of all portions of the pegmatite except the dark marginal zone of sizes ranging from that of a walnut up to that of a man's head ; fluorite octahedra, sometimes of large size ; and a thickly felted mass of a delicate, grayish-blue crocidolite filled with minute hair-like crystals of riebeckite. The crocidolite embeds, more or less completely, the quartz and rock fragments."

Literature:

Charles H. Warren and Charles Palache(1911): The Pegmatites of the Riebeckite-Aegirite Granite of Quincy, Mass., U. S. A.; Their Structure, Minerals, and Origin, Proceedings of the American Academy of Arts and Sciences, Vol. 47, No. 4 pp. 125-168

Arthur Wellington Brayley(1913): History of the Granite Industry of New England, Volum 1, National Association of Granite Industries of the United States

BK Emerson (1917): The geology of Massachussetts and Rhode Island, USGS Bulletin 597

Paul C. Lyons (1972): Significance of riebeckite and ferrohastingsite in microperthite granites, Am. Min Vol. 57, pp.

Sayer, Susan (1974): An Integrated Study of the Blue Hills Porphyry and Related Units, Quincy and Milton, Massachusetts (MIT master's thesis)

Paul C. Lyons (1976): The chemistry of riebeckites of Massachusetts and Rhode Island, Min. Mag Vol 40, pp 473-479


Riebeckite
USA
New Jersey , Somerset Co., Warren Township, Stirling Brook ("Carnelian Creek")

Riebeckite 4,5cm specimen	© BDP

Silicified crocodilite is found in a creek with carnelian and other minerals, see Mindat message board for further details.

Magnesioriebeckite
USA
New Jersey , Sussex Co, Franklin Mining District, Franklin



Magnesioriebeckite is a rare mineral at the Franklin mining district, but it is found in two different paragenesis; One in relation to the ore-body at Franklin hill where it was found as up to as 4-cm dark green prismatic crystals associated with rhodonite, calcite, and franklinite.

The other known occurance has been described by Palache (1928) when light blue fibrous masses was found on the Trotter Dump in 1906, where magnesioriebeckite was found with willemite, sphalerite and blue calcite. Some specimens have small corroded remants of aegirine, and some was found with serpentinite. Although the exact assemblage and in-situ relationship is not known it is apparent that magnesioriebeckite is a late stage mineral at Franklin

Literature:

Pete J. Dunn (1995): FRANKLIN AND STERLING HILL, NEW JERSEY: THE WORLD'S MOST MAGNIFICENT MINERAL DEPOSITS



Olav Revheim May 2012

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Edited 21 time(s). Last edit at 06/24/2012 03:39AM by Alfredo Petrov.

Olav,
Image number 44803 is used to illustrate both Magnesioriebeckite-Riebeckite Series (Var: Crocidolite) from
Pomfret Mine, Vryburg, Northwest Province, South Africa as well as Magnesioriebeckite-Riebeckite Series
(Var: Crocidolite) from USA, Massachusetts , Norfolk Co , Quincy, Granite Rail Quarry (Granite Railway Quarry).

Rock Currier
Crystals not pistols.

Oops, cut and paste error. Thanks for spotting



Olav

Yes, I understand, I hate it when that happens to me.

Rock Currier
Crystals not pistols.