Winchite series

First Draft

Winchite Series

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The winchite 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:

Ferri-ferrowinchite
☐ (NaCa) (Fe2⁺₄Fe³⁺)Si₈O₂₂(OH)₂

Ferriwinchite
☐ (NaCa) (Mg₄Fe³⁺)Si₈O₂₂(OH)₂

Ferrowinchite
☐ (NaCa) (Fe²⁺₄Al)Si₈O₂₂(OH)₂

Parvowinchite
☐( NaMn²⁺) (Mg₄Al)Si₈O₂₂(OH)₂

Winchite
☐( NaCa) (Mg₄Al)Si₈O₂₂(OH)₂

The winchite-series minerals has an internediate composition between the tremolite-actinolite series and the glaucophane-series minerals.It should be noted that the definition of the mineral does not entirely fit with it's chemical formula. Given it's intermediate composition, it's rarity and somewhat unclear definition it seems appropriate to discredit all of the minerals in the series. That being said, the winchite series minerals are approved minerals that has been identified from several localities and they deserve a place in any systematic collection.

The winchite series minerals are in the somewhat self-contradicting position of being both more common and more rare than originally believed. It is more common as rims and zones in multi-zoned amphiboles in many rocks from multiple world wide localities, but it is rarer as a collectible mineral than we mineral collectors would like to hope. This article started out with more localities and better specimens than has been included in the first draft version, and it has in many ways become more of a "these are not winchites afterall" article, as the most attractive winchites in the Mindat galleries appears not to be winchites, but rather other amphiboles.

The yellowish, transparent amphiboles from the Koksha valley in Afghanistan has been marketed as winchite, but the few analysis that has been made on this material indicates that these amphiboles are richterite-series minerals rather than winchite.

The manganoan cummingtonites of Talcville New York is often named parvowinchite. This incorrect naming is based on an misunderstanding of the name tirodite. Several analysis is made on this material and both the Al content and Na content is way too low for these amphiboles to be anything else than a Mn-rich cummingtonite. It is also difficult too see how the geological environment at this locality could support an alkali-rich amphibole.

The known, confirned occurances of winchite are all from multi-amphibole environments, and unless accompanied with a confirmed analyisis of the exact same material, the identification of a mineral as winchite will always be tentative, possibly speculative.

Winchite
India
Madhya Pradesh, Jhabua District, Kajlidongri mine

Winchite FOV 12x10 mm	© Pavel M. Kartashov

Winchite was first identified from the Kajlidongri manganese mine in 1904, and was named after it's finder, Mr. H. J. Winch by Sir Lewis Fermor who gave the first description of the mineral. "Winchite" occurs as cobalt blue to bluish-violet stout prismatic crystals, thin fibres, blades, acicular prisms, and also in rosettes. The longest prismatic crystal measured was 4 cm long. There are also spherulitic forms with cores of pyroxene fibres with peripheral winchite. The mineral occurs in schist containing braunite and calcite, in quartzite, manganiferous quartzite with pyroxene, pyroxene-bearing quartzite, and a lavender to ash-grey friable sandy rock.

The amphibole is especially developed in the schist that forms a 1"5 m band conformable with the ore body, and forms one wall in the north-east part of the mine. These rocks are termed "gondites" and are of metasedimentary origin and belongs to the Aravalli Supergroup (2300Ma). The geology and paragenesis is described by Ray et.al (1963) and Ost
wald and Nayak(1993).

In 1971, Lahiri published a new analysis of the winchite from Kajlidongri. This analysis deviated from Fermor's analysis in that the analysed amphibole had a " composition (that) would be some form of eckermannite or magnesioarfvedsonite" according to Nayak/Leake 1975 who confimed Lahiri's analysis of the blue amphibole as magnesioarvfedsonite and the winchite became "winchite".It was however difficult to find any obvious error in Fermor's work, and a "hunt" for an amphibole matching the original winchite started.

In 1981, Leake et.al. published analysis' of several of the blue Kajlidongri amphiboles, many with the same physical and optical properties as the material analysed as winchite by Fermer. From this material tremolite, "tirodite", magnesio-arfvedsonite, manganoan eckermannite and magnsioriebeckite was identified, but no winchite.

In 1986, a successful rediscovery of winchite from the type locality was published. Winchite was identified in a "Crystal T2 (which) is 0.3 mm in diameter and is strongly zoned, as are most of the amphiboles at this locality. It varies from a 0.04 mm sodic-calcic centre to a calcic outside but the centre falls into the winchite field of the IMA classification" Leake at al (1986).

From all this, the conclusion can be drawn that almost all the blue/purple/lilac amphiboles form Kajlidongri are zoned and contains multiple amphibole species, and that they probably not contain winchite.

Literature:

Supriya Roy, Fanindra Nath Mitra (1963):Mineralogy and genesis of the gondites associated with metamorphic manganese ore bodies of Madhya Pradesh and Mahahashtra, India, Proc.nat.Inst.Sci. India, Vol 30

J.Ostwald and V.K.Nayak(1993): Braunite mineralogy and paragenesis from the Kajlidongri mine, Madhya Pradesh, India- Mineral Deposita 28, pp153-156

V. K. NAYAK, BERNARD E. LEAKE (1975): On 'winchite' from the original locality at Kajlidongri, India. MINERALOGICAL MAGAZINE VOL. 40, PP. 395-9

Bernard E. Leake, Colin M. Farrow, V.K.Nayak (1981): Further studies on winchite from the type locality, American Mineralogist, Volume 66, pages 625-631,

B. E. LEAKE, C. M. FARROW, F. CHAO, V. K. NAYAK(1986): Winchite re-discovered from the type locality in India, MINERALOGICAL MAGAZINE,VOL. 50, pp 173-175

Parvowinchite
India
Madhya Pradesh, Tirodi ,Tirodi Mine

Parvowinchite 6,3cm specimen	© Weinrich Minerals, Inc.

Mn-bearing alkali amphibole is common among the Mn-bearing amphiboles present in gondites of Madhya Pradesh and Maharashtra, India. Gondites are regionally metamorphosed manganiferrous sedimentary rocks, characterized by spessartine and quartz with or without other manganese silicates, such as rhodonite and manganiferrous pyroxenes and amphiboles, interbedded with other (pelitic and psammitic) sedimentary rocks. The Mn ore minerals (braunite, bixbyite, hollandite,hausmannite, jacobsite, etc.) associated with gondites are almost entirely of metamorphic origin

At Tirodi, a Mn-rich alkaline amphibole was described as tirodite in 1938. The name tirodite was later used for also other Mn-rich amphiboles without the high alkali content found in the amphiboles from Tirodi, and the name tirodite was later defined as a manganocummingtonite before it was finally discredited in 1997. These changes in names and meaning of names has been confusing for both collectors and mineralogists, and the Mn-rich alkali-amphibole was christened parvowinchite in 2003, and there are reaons to believe that this may not be the final name assigned to these amphiboles.

Parvowinchite is the "original" tirodite, and it occurs as fine straw yellow needles or blades associated with rhodonite,spessartine, and manganese oxides associated with the gondites. Large prismatic crystals of parvowinchite (up to 25 cm in length, as in the Tirodi West Hill pegmatites) occur in Tirodi where pegmatites cut across gondites and Mn-ore bodies. These occurrences are restricted to the sillimanite zone.

Literature:
Yen-Hong Shau, Donald R. Peacor, Subrata Ghose, P.P.Phakey (1993): Submicroscopic exsolution in Mn-bearing alkali amphiboles from Tirodi, Maharashtra, India, American Mineralogist, Volume 78, pages 96-106,

Curt G. Segeler (1961): First U.S. Occurence of manganoan cummingtonite, tirodite. American Mineralogist VOL 46

Supriya Roy, Fanindra Nath Mitra (1963):Mineralogy and genesis of the gondites associated with metamorphic manganese ore bodies of Madhya Pradesh and Mahahashtra, India, Proc.nat.Inst.Sci. India, Vol 30


Ferrowinchite
Sweden
Värmland, Filipstad , Persberg district , Pajsberg, Harstigen Mine



The Harstigen mine is a small manganese mine operated in two period in the 19th century. The ore is of the Långban type with a complex Mn and Fe skarn mineralization. Although the Långban mine is more widely known, Harstigen is a very interesting locality. 148 minerals have been identified here, and 10 minerals have Harstigen as their tyope locality. Not bad for a 33m deep mine with a total production less than 500t ore.

According to Nysten and Skogby, "The winchite phase occurs fairly abundantly in a restricted association, consisting of a dark green clinopyroxene intergrown with fine-grained hematite and yellowish-brown andradite. This matrix is
cut by distinctly later veinlets of rhodonite, occurring as euhedral crystals embedded in fibrous to radiating ferro-ferri-winchite and minor baryte, galena, and calcite."

Ferri-ferro winchite occurs as actinolite-like spherical aggregates up to 5 mm in size.

Per Nysten, Henrik Skogby (1994): Manganese ferro-ferri-winchite from Harstigen, Filipstad, central Sweden, Mineralogical Magazine, Vol 58,pp 168-172

Olav Revheim March 2012

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Edited 11 time(s). Last edit at 03/26/2012 09:04AM by Olav Revheim.

Olav,

Good for you. In a month or two I hope to get back into working on the Best Minerals articles.

Rock Currier
Crystals not pistols.