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Posted by Olav Revheim  
October 11, 2011 12:00PM
First Draft

Click here to view Best Minerals G , and here for Best Minerals A to Z and here for Fast Navigation for finished Best Minerals articles.

Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?



PermanganogruneriteMn2Mn5Si8O22(OH)2 ( Hypotetical end member)

Gruenerite Individual crystals to 1,7cm, Helen MacLeod Mine, Ontario, Canada

The grunerite and manganogrunerite amphiboles belong to the "Mg-Fe-Mn-Li Clino-Amphibole Subgroup" and forms the Fe-rich members in a continuous series with cummingtonite and manganocummingtonite. The hypotethical end mamber permanganogrunerite forms the Mn-rich end member in this series. Gedrite are polymorph with the orthorombic ferroanthophyllite, and does occationally occur together with this mineral, such as at Rockport, Massachusetts, USA.

Grunerite are also closely related to ferroactinolite ( where Ca replaces Fe in the B position), but does not seem to accept any significant Ca in it's structure as actinolite are sometimes found as exclusion lamellea in gedrite samples.

Grunerite and manganogrunerite are quite common in precambrian banded iron formations (BIF) when these are methamorphosed to amphibolite facies. In these cases grunerite is a rock forming mineral and can be found throughout large areas, such as the Labrador and Lake Superior areas of North America, in Australia and in Sweden together with other iron minerals such as magnetite, Fe-carbonates ( siderite) and various iron silicates, often also near chert or jasper. Manganogrunerite occurs in the same areas and same geological environments, when these are enriched in manganese.

Grunerite-series minerals normally occurs as small shiny fibres in the rock, but can occationally form crystalline mats or stars. The dm-long fibrous aggregates from Penge in South Africa are rather unique, but will never form especially attractive mineral specimens. These asbestos-like fibrous aggregates are called amosite, and this is othen considered a synonym or variety of grunerite. This is not exactly the case, as the name amosite has also been used for riebeckite found in the same geological province.

Dannemorite is an old name for manganoan grunerite that has been used as an synonym for manganogrunerite, and even in some recent texts, the name dannemorite are used. Even though dannemorite are used when the grunerite contains some Mn, it does not always contain sufficient amounts to qualify as manganogrunerite.

The entries includedd in this article does not necessarily reflect "the best" grunerite series minerals, but rather typical occurances.

Grunerite Manganogrunerite Austalia New South Wales, Yancowinna Co., Broken Hill

Grunerite-series (Broken Hill North mine), 7mm FOV

Broken Hill is one of the really iconic mineral locations in the world, not just for the tremendous wealth of mineral species, some of them highly desired by collectors. It has also supplied Australia with hundreds of millions ton of ore and it has given its name to a distinctive type of ore deposits, the Broken Hill type. It is also thoroughly described in the geological literature. It does seem that scientists does not fully agree on the ore deposits origin, but it is apparent that the Broken Hill ore deposits are stratabound, highly metamorphosed ( amphibolite/granulite facies) rocks .

Manganogrunerite and grunerite are predominantly found as a rock forming mineral together with magnetite, garnet, (mangano?)cummingtonite and other minerals in a stratabound magnetic iron formation associated with the ore mineralization, and should therefore be present in most if not all of the ore locations in Broken Hill.

Given it’s mode of occurance as a rockforming mineral in a fine grained highly metamorphosed rock, one cannot expect to find any outstanding specimens. A solid solution series exists between the manganogrunerite, grunerite, cummingtonite and manganocummingtonite, and a quantitative chemical analysis is required to correctly identify a specimen.

S.G. Walters(1998): Broken Hill-type deposits, AGSO Journal of Australian Geology and Geophysics, 17(4), 229-237

Wolfgang R. Leyh , Colin H.H. Conor (2000): Stratigraphically controlled metallogenic zonation associated with the regional redox boundary of the Willyama Supergroup, MESA Journal 16 January 2000

Tim Hopwood (2007):Geology and Potential Mineral Resources of the Pinnacles Mine,Broken Hill, NSW, Australia. Geological report prepared for Pinnacles Mines Pty Ltd,

Manganogrunerite Austria Styria, Neumarkt, Dürnstein , Mn deposit

Manganogrunerite 10cm FOV

Grunerite Canada Newfoundland and Labrador , Labrador, Smallwood Mine

Grunerite 4 cm FOV

The production of iron ore from the Smallwood mine started in 1962, and it soon became one of the world’s largest iron ore producers. Still today a significant portion of the world’s iron ore is produced from the Wabush Iron Formation in the Labrador Through.

The Wabush Iron formation is a meta-sedimentary Precambrian ore metamorphosed to granulite facies during the Grenville orogeny. The Wabush formation consist of two units, the lower Wabush iron-formation consisting of quartzcarbonate-silicate-magnetite rocks, and the upper Wabush iron-formation consisting of quartz-specularite-magnetite rocks. It is the upper formation that are most economically interesting.

Members of the cummingtonite-grunerite series are the most abundant silicates in the metamorphosed wabush iron-formation. Grunerite occurs both in the lower and upper wabush iron-formation as small to coarse prismatic grains or fibrous needles associated with quartz, carbonate, magnetite or other silicates. The color range from near colorless via amber to brown.

Most often the chemical composition of the cummingtonite-grunerite falls within the grunerite range, but may also be ferroan cummingtonites. It should be noted that a manganocummingtonite ( always low Fe) and anthophyllite occurs in the upper Wabush formation, although not directly associated with grunerite.

K. L. CHAKRABORTY(1963): Relationsship of anthophyllite, cummingtonite and manganocummingtonite in the metamorphosed Wabush Iron formation Labrador.

Cornelis Klein Jr. (1966): Mineralogy and Petrology of the Metamorphosed Wabush Iron Formation, Southwestern Labrador, Journal of Petrology Volume7, Issue2 Pp. 246-305.

Takashi Miyano and Cornelius Klein (1983): Phase relations of orthopyroxene, olivine, and grunerite in high-grade metamorphic iron-formation, American Mineralogist, Volume 68, pages 699-716

Grunerite Canada Ontario, Algoma District, Chabanel Township, Wawa, Helen - MacLeod Mine

Grunerite Individual crystals to 1,5cm

The Helen-Mac Leod mine was originally two separate mines extracting iron ore ( predominantly siderite) from 1939 until 1998. Totally more than 100 million tons of siderite was produced from a more than 2 km long ore body.

In geological terms , this orebody belongs to the pre-cambrian Michipicoten group and consists of metamorphosed flows and pyroclastic rocks of andesite-rhyolite composition together with zones of clastic sediments and banded iron formations. The banded iron formations consists of chert, pyrite and carbonate(siderite) layers and are believed to have originated from large-scale hot-spring and fumarolic activity.

Although described as a one-time find from the Helen-Mac Leod mine, grunerite has been described as “spheroids of radiating fibres” from the magnetite bearing chert layers elsewhere in the Michipicoten group, thus verifying the EDS analysis performed on the pictured specimens. It appears that the individual crystals reach sizes up towards 2cm.


A.M. Goodwin(1962): Structure, Stratigraphy, and Origin of Iron Formations, Michipicoten Area, Algoma District, Ontario, Canada, Geological Society of America Bulletin, May 1962, v. 73, no. 5, p. 561-586,

E.D. Frey, R.P. Sage ( Editors)(1987): Proceedings and abstracts for 33rd Annual Meeting, Wawa Ontario, part 1 &2. Ontario Ministry of Northern Development and mines

Charles Richard van Hise and Charles Kenneth Leith (1911):The geology of the Lake Superior region, United States Geological Survey

Grunerite Portugal Vila Real District, Vila Real, Vila Cova Mine

Grunerite 60mm FOV

The Vila Cova mine is an abandoned iron mine where matemorphic stratiform magnetite ore was extracted. Grunerite occurs as silvery, shiny fibres as an accessory mineral associated with the 3-35cm thick magnetite layers.


Nuno Sousa (2010)

Grunerite South Africa Limpopo Province, Penge Mine

Grunerite 8cm specimen

Grunerite occurs as a rock forming mineral in several horizons in the Penge Iron Formation. This formation is a sedimentary sequence consisting of banded iron formations, cherts, clays and carbonate rocks. It was intruded by magmas belonging to the Bushveld complex 2050-2062 MA, which metamorphosed the the slightly folded Penge Formation to a variable degree.

Grunerite occurs as fibrous to acicular rosettes, or prismatic subhedral crystals, and coexists with almost all the other minerals present in the iron-formation. Grunerite grains in biotite hornfels and magnetite–grunerite banded iron-formation commonly contain minute inclusions of kerogen. Idioblastic prisms of grunerite are sometimes surrounded by blue riebeckite and replace larger grains of magnetite. In high stress areas, such as at the synclinal and anticlinal areas of the folds, gruenerite forms asbestifom bands in the rock. These bands can be up to 3m thick and the individual grunerite asbestos fibres may reach several dm.

Near Penge, these fibres are predominantly grunerite. At at other locations in the same formation, such as Mafefe, riebeckite is more common. Gruenerite replaces riebeckite in areas exposed to higher temperatures during metamorphosis.


T. MIYANO and N. J. BEUKES (1997): Metamorphosed Amphibole Asbestos-bearing Penge Iron Formation, Eastern Transvaal,South Africa, JOURNAL OF PETROLOGY VOLUME 38 NUMBER 5 PAGES 651–676

Manganogrunerite Sweden Västmanland, Hällefors, Grythyttan, Brunsjö Mine (Brunnsjö Mine)

Manganogrunerite, 4x4mm FOV

Bergslagen is a mining district in central Sweden that has been a major metal producer for well over 1000 years and which contains over 6000 ore deposits and mineral prospects. By far the most common type of metallic mineral deposit in Bergslagen consists of Fe oxide with variable amounts of Mn in associated skarn and crystalline carbonate rocks. More than 2000 of these deposits are known, most of which are small and, since the middle of the 19th century, without any economic significance.Many of them contain amphiboles in the cummingtonite-grunerite-manganogrunerite series.

The Mn-rich depoits are to a large extent, hosted by crystalline carbonate (marble) horizons. They are generally stratbound to stratiform and lens-shaped and metamorphosed to amphibolite-facies ( locally granulite). The Fe oxide deposits associated with Mn-rich skarn or crystalline carbonate rock commonly contain magnetite and manganiferous calc-silicates, including pyroxene, dannemorite (manganogrunerite) , knebelite and spessartine-rich garnet. The Brunnsjö Mine is included as a typical location, rather than the "best" of manganogrunerite locationd amongst the many other in the area, The Dannemora district ( type locality of dannemorite) is one of the others.

The presence of manganogrunerite at the Brunsjö mine is confirmed in the Handbook of Mineralogy, and fibrous aggregates reaching several cm in length are known. Manganese grunerite from these locations are often described as “dannemorite”, even today. The "dannemorite" does not always contain sufficient Mn to qualify as manganogrunerite. These Fe-oxide ore bodies also contain cummingtonite, anthophyllite, actinolite-tremolite and grunerite, so that care should be taken in assigning a name to any of the amphiboles from the Bergslagen mining area.


Nils Jansson& Rodney Allen (2010): The origin of iron ores in Bergslagen and their relationships with polymetallic sulphide ores, Sveriges geologiska undersökning, Forskning och Utveckling SGU-rapport 2010:5

Rodney Allen, Magnus Ripa, Nils Jansson (2008): Palaeoproterozoic volcanic- and limestone hosted Zn-Pb-Ag-(Cu-Au) massive sulphide deposits and Fe oxide deposits in Bergslagen,Sweden. 33 IGC excursion No 12, August 14 – 20

Dannemorite, Handbook of Mineralogy.

Grunerite USA Michigan, Dickinson Co., Menominee iron range , Randville , Groveland Mine

Grunerite, 7 cm specimen

The Groveland Mine was one of the four main mines operated in the West Menominee Range of northern Michigan. It lies four miles west of Randville in the 1 mile wide and 15 miles long Felch Iron District, and was shut down in 1982. Large volumes of siliceous grade magnetite and hematite ore has been yielded from this district from a banded iron formation.

Grunerite is found as a rock-forming mineral in several of the Fe-enriched horizon in the highly metamorphosed 1,9-2,1 Ga old sedimentary rocks. It occurs as silvery fibres embedded in the rock, or as thin seams together with magnetite, hematite and jasper. Being a rock forming mineral it can be found the mine tailings as well as several outcrops in the area. In addition to grunerite, also actinolitic and hornblendic amphiboles can be found in this rock sequence, although grunerite is the more common amphibole in the iron horizons



GEOLOGY OF CENTRAL DICKINSON COUNTY MICHIGAN By H L James L D Clark C A Lamey and F J Pettijohn In collaboration with Jacob Freedman James Trow and KL Wier GEOLOGICAL SURVEY PROFESSIONAL PAPER 310- 1961

John T. Cumberlidge and John G. Stone(1964): The Vulcan iron formation at the Groveland Mine, Iron Mountain, Michigan- Abstract, Economic Geology; v. 59; no. 6; p. 1094-1106

Grunerite USA Michigan, Marquette Co., Marquette iron range, Michigamme , Michigamme Mine (Mt Shasta mine)

Grunerite, 1 cm crystals

The Marquett iron range show many simulariteis with the nearby Menominee iron range, and the presence of grunerite is closely attached to the metasedimentary banded iron formation, the Negaunee iron formation. The Neganuee iron formation is classified both from variable metamorphic conditions as well as rock horizons, but are mainly considered a “magnetite-grunerite” ore.

Grunerite occurs in particular in the higher metamorphic grade rocks on the interface between ferruginous and the siliceous layers. The grunerite may occure as microscopic fibres, but more commonly as 2-6 or larger fibres, often as rosettes. As grunerite is a rock forming mineral it may be found in several mines in the area, as well rock outcrops and road cuts.
The Michigamme mine was operated from 1870-1901, and produced almost a million tons of iron ore. Minerals can still be found in the tailings.


William F. Cannon (ed) (2003): Part 2- Field Trip Guidebook, Iron Mountain, Michigan, Proceedings Volume 49 INSTITUTE ON LAKE SUPERIOR GEOLOGY

Natalie Pietrzak (2011) : The Complex Paragenetic History of Basal Negaunee Iron Formation Iron Ores,Tilden Mine, Marquette District, Upper Michigan, Graduate Program in The University of Western Ontario London, Ontario, Canada

C. Stephen Haase (1982):Metamorphic petrology of the Negaunee Iron Formation, Marquette District, northern Michigan; mineralogy, metamorphic reactions, and phase equilibria- Abstract, Economic Geology; v. 77; no. 1; p. 60-81

BURTON H. BOVUM (1964):The Marquette Mineral District Michigan, THE CLEVELAND-CLIFFS IRON COMPANY PAPER


Olav Revheim nov 2011

Click here to view Best Minerals G , and here for Best Minerals A to Z and here for Fast Navigation for finished Best Minerals articles.

Edited 13 time(s). Last edit at 03/26/2012 11:54AM by Rock Currier.
avatar Re: Grunerite-series
October 12, 2011 06:05AM
I did a bunch of borates and they truly needed a champion if any mineral did. I am glad the you are doing Gruneirte. No one can accuse us of picking out only the pretty minerals I guess.

Rock Currier
Crystals not pistols.
avatar Re: Grunerite-series
October 12, 2011 12:20PM
Hello Olav - the material from Wawa Ontario was acquired from an Ontario dealer in 2010 - at the time he advised that the grunerite had been ID'd by EDS and that it was from "a one-time find".

Hope this helps
Re: Grunerite-series
October 12, 2011 07:44PM

Thank you very much for your input. Knowing how these amphibole entries are identified are very importnt to me, as they are so horribly difficult to distinguish from each other. The combination of your input and the literature references should, I think, ID these specimens "beyond reasonable doubt".

The literature references might, by the way, be worthwhile to download, especially the 756 pages volume: "The geology of the Lake Superior region" should be interesting to browse through if you do not live too far away from the region.


avatar Re: Grunerite-series
October 12, 2011 07:57PM
Hi Olav - glad I could help.

Thanks for the reference lead. We live about 10 - 12 hours away by car (with several comfort breaks on the way!) - hope to make a trip to the region next summer!

Re: Grunerite-series
October 12, 2011 08:03PM

When I started to do the amphibole group just over a year ago, I didn't think it was going to be pretty. >:D<

On the other hand I must admit that there are more nice looking amphiboles out there than I had ever believed, and a year into my amphibole project I think that I am slowly getting to understand and appreciate the diversity and complexity of this particular group of minerals.

In doing so I am, one small step at the time, achieving my learning objective for doing this.


avatar Re: Grunerite-series
October 13, 2011 01:57PM
I agree, doing the best minerals articles is a great learning experience.

Rock Currier
Crystals not pistols.


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