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Amphibole-Group Minerals From New York State

May 14, 2008

By Lupulescu, Marian

Readers may wonder why we need an article about amphiboles in this publication. There are considerable concerns about this topic, and I want to comment briefly about two of them. With some exceptions, many mineral lovers consider the amphibole-group minerals not spectacular enough to be collected and displayed; indeed, they believe these dark minerals are significant only for professional mineralogists who like to classify them in groups and species or for the petrologists who use them for fluid modeling or geobarometry. Another concern, probably the most important, is related to the amphibole nomenclature itself. I agree that for some mineral collectors it is difficult to deal with the newly introduced names and prefixes established by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA). However, the amphiboles are rich in chemical and structural complexity, and an appropriate nomenclature must reflect this. I disagree with the usefulness of such a statement as “when I see a black, prismatic silicate mineral in an Adirondack gneiss, I’m still going to call it hornblende” (Kelly 2004). According to Leake et al. (1997), “the familiar word hornblende can still be used where appropriate for calcic amphiboles . . . because hornblende is never used without a prefix . . . . In the precise classification, such confusion should not arise between colloquial use and precise use.” The “black, prismatic silicate mineral” has a name, hastingsite, that has been in use for years (Gallagher 1937; Buddington 1939; Leonard 1951; Buddington and Leonard 1953) and is still accurate. We cannot call all of the minerals from the amphibole group “hornblende” because this does not indicate enough about the real geologic environment where the mineral formed. Would it not be better to simply call them “amphibole”? I also have to disagree with the above statement because we owe our respect to the group of scientists who worked very hard for many years to give us the actual nomenclature; their efforts should not be minimized.

In this article, I hope to convince the concerned reader that the amphiboles are sufficiently spectacular and interesting to be collected, studied, and displayed for public delight in museums, that the use of the new amphibole nomenclature is really not so complicated, and that the new names and prefixes relate closely to the environment where the amphiboles are found. The names of the mineral species listed below, and their prefixes, are in accordance with IMA amphibole nomenclature (Leake et al. 1997; Leake et al. 2003; Burke and Leake 2004; Bayliss, Kaesz, and Nickel 2005).

The New York State Museum has a large and beautiful collection of amphiboles from across the state, exhibited in the “Minerals of New York” section of the Museum’s Adirondack Hall (fig. 1). Presentation of the finest amphibole specimens from this collection is the main focus of this article. The mineral species were identified by their chemical compositions as determined by electron microprobe.

Species Descriptions

Group One: Mg-Fe-Mn-Li Amphiboles

Anthophyllite, Mg^sub 7^Si^sub 8^O^sub 22^(OH)^sub 2^, is reported from the Jayville iron deposit (Leonard 1951; Leonard and Vlisidis 1960) and is associated with or possibly replacing tremolite at Edwards (Rabbit 1948) and Balmat (Brown and Engel 1956), all in St. Lawrence County. Anthophyllite occurs in a fibrous habit in specimens from Manhattan, New York County; as stellate, fibrous aggregates (Manhattan); in columnar arrays (Swan Street, Richmond County); massive (Edwards, St. Lawrence County); spherulitic (Fifty-ninth Street, New York County); as plumose fibrous aggregates (New York County); and as asbestiform aggregates (Manhattan, Quarantine and Grymes Hill, both on Staten Island, Richmond County, and at Tilly Foster mine in Putnam County). The acicular to fibrous crystals of anthophyllite to 40 cm long are a brownish-gray color or are colorless.

Cummingtonite, Mg^sub 7^Si^sub 8^O^sub 22^(OH)^sub 2^, was found at the Arnold pit and at talc mines in Talcville, both in St. Lawrence County. It occurs as coarse, subhedral, bladed crystals (fig. 2) to 12 cm, displaying parting perpendicular to the c-axis, randomly distributed in a matrix of fine acicular crystals in parallel arrangement of cummingtonite or tremolite (either colorless tremolite or lavender “hexagonite”). It also occurs as compact masses of bladed crystals or as radiating aggregates. Some of the specimens from the International No. 3 Talc mine (Talcville) display multiple twins on {100}, have a pale pink color, and contain some calcium and manganese (Mn-rich cummingtonite). Segeler (1961) described the “manganoan cummingtonite,” to which he assigned the name “tirodite” (IMA’s manganocummingtonite species), from the International Talc Company mine at Talcville, as “bladed pink crystals an inch in width and up to three inches long” that were embedded in “light pink fibrous masses.” Some of the Mn-rich cummingtonite crystals from Talcville fluoresce bright orange (fig. 3) in shortwave ultraviolet radiation and pale orange in longwave ultraviolet radiation (calcium 0.50 apfu [atoms per formula unit] and manganese 0.90 apfu) or bright red in shortwave and pale red colors (calcium 0.11 apfu and manganese 0.42 apfu) in longwave ultraviolet radiation.

Manganocummingtonite (“tirodite”), Mn^sub 2^Mg^sub 5^Si^sub 8^O^sub 22^(OH)^sub 2^, has also been reported at the Wight mine and Gouverneur Talc mine, Balmat, in massive aggregates of millimeter- sized pale brown crystals and in the Talcville area (Robinson and Alverson 1971), all in St. Lawrence County.

Group Two Calcic Amphiboles

Actinolite is no longer considered a valid mineral species according to the IMA amphibole nomenclature (Leake et al. 1997), but the name is still used extensively by metamorphic petrologists. The description of the green to dark green mineral species-still referred to as actinolite by petrologists-is found under tremolite.

Chloro-potassichastingsite, KCa^sub 2^(Fe^sup 2^^sub 4^+Fe^sup 3^+)Si^sub 6^Al^sub 2^O^sub 22^Cl2, is not a very common mineral. Leger, Rebbert, and Webster (1996) mentioned this species for the first time from New York in a gneiss from the Black Rock Forest, Cornwall, Orange County as “the most Cl-rich amphibole, a hastingsite.” I identified it from the O’Neil iron mine in Orange County as both large (to 2-cm), cleaved, and broken crystals and in thin sections.

Edenite, NaCa^sub 2^Mg^sub 5^Si^sub 7^AlO^sub 22^(OH)^sub 2^, was reported by Beck (1842) and Buerger (1927) at Edenville and by Cosminsky (1947) at the Atlas quarry, both in Orange County. Edenville is considered the type locality for the mineral (fig. 4). It was not analyzed in the original description, and the two analyses on topotype material reported by Rammelsberg (1858) in Leake et al. (1997) and Hawes (1878) differ, and neither plots in the edenite range (Leake et al. 1997). I analyzed many “edenite” specimens from across New York, and especially from the Franklin Marble in Orange County, and found that only a few of them fall in the edenite compositional field; all others are fluoro-edenite. I identified the mineral from Edenville, Amity, and the Lewis iron mine in Orange County, from the Mineville mining district in Essex County, and from the Phillips iron mine in Putnam County. The most spectacular specimens come from Edenville and Amity. They are short, terminated prisms to 3 cm with a greenish-gray color associated with phlogopite and graphite in Franklin Marble. All the specimens contain fluorine in considerable amounts but not enough to make them fluoro-edenite. The amount of fluorine in the edenite composition might be related to the degree of metamorphism, for it is known that the replacement of (OH)- by F- stabilizes the mineral at higher- grade metamorphic conditions. The specimens from the iron mines have some potassium in their composition.

Ferro-actinolite, Ca^sub 2^Fe^sub 5^^sup 2^+Si^sub 8^O^sub 22^(OH)^sub 2^, occurs in massive aggregates with a bluish tint at Mineville, Essex County, and in fibrous masses at the Tilly Foster mine, Putnam County. Fragments of bladed ferro-actinolite to 10 cm in length have been collected at Power’s farm in Pierrepont, St. Lawrence County. Chamberlain, Robinson, and Smith (1987) reported the “bluish uralitization” on the diopside from the Farr property at Natural Bridge also as ferro-actinolite.

Ferro-edenite, NaCa^sub 2^Fe^sub 5^^sup 2^+Si^sub 7^AlO^sub 22^(OH)^sub 2^, has been found as millimeter-sized crystals in the iron deposits from Mine- ville, Essex County, and the Surebridge and Black Ash mines, both in Orange County. The mineral contains large amounts of fluorine, from 0.53 (Black Ash mine) to 0.92 apfu (Surebridge mine).

Ferropargasite, NaCa^sub 2^(Fe^sup 2^^sub 4^+Al)Si^sub 6^Al^sub 2^O^sub 22^(OH)^sub 2^, has been found as large, well-developed crystals flattened on {010} at Cascade Slide, Essex County (fig. 5), in a fibrous habit in the Town of Moriah, Essex County, as euhedral crystals at Edenville, and as clusters of crystals at Warwick, both in Orange County.

Fluoro-edenite, NaCa^sub 2^Mg^sub 5^Si^sub 7^AlO^sub 22^F^sub 2^. At the 2001 Rochester Mineralogical Symposium, Dr. Scott Ercit noted the first occurrence of fluoro-edenite in New York at the McLear pegmatite, DeKalb, St. Lawrence County. Since then, my survey of the amphibole-group minerals from New York has extended the number of fluoro-edenite occurrences. I identified the mineral from Edenville, the Atlas quarry, and the Walling Road occurrence in Orange County, and at the Lyon Mountain and Rutgers iron mines in Clinton County. Fluoro-edenite from Edenville (fig. 6) was confused for a long time with edenite because both have similar crystal morphology and optical properties. Here, they are short prismatic crystals to 2 cm of pale gray-brown or gray-green color, randomly scattered in marble matrix associated with phlogopite that develops along the crystal faces and cleavages. The mineral from Walling Road is bright green without crystal faces but with conchoidal fracture. At the Atlas quarry, fluoro-edenite is colorless or pale gray and is easily confused with fluorotremolite, which also occurs here. It also has the same fluorescent colors as fluorotremolite (confusion is compounded by the intimate parallel growth between these two minerals). The fluoro-edenite from Rutgers mine forms short stubby, dark green to black prisms to 0.5 cm associated with magnetite. Large etched crystals of fluoro-edenite to 1 foot long were reported as “hornblende” by Whitlock (1907) and as hastingsite by Gallagher (1937) from the Chateaugay mine at Lyon Mountain. Fluoropargasite, NaCa^sub 2^(Mg^sub 4^Al)5(Si^sub 6^Al^sub 2^)^sub 8^O^sub 22^F^sub 2^. We des-cribed this mineral from the type locality at Edenville, Orange County, and also identified specimens from Russell, St. Lawrence County, and Monroe, Orange County (Lupulescu et al. 2005). It was mentioned initially by Kearns et al. (1980) in the Franklin Marble in Orange County but without the name fluoropargasite. The holotype specimen (NYSM 338.92) from Edenville is a 13 x 7 x 4.5- cm stubby, black, prismatic crystal (fig. 7) associated with calcite, dark green tremolite, titanite, and phlogopite, all developed along cleavages and/or crystal faces. Another specimen from Edenville, in the A. E. Seaman Mineral Museum collection (DM 17326), has only titanite and diopside in association. Fluoropargasite from Russell occurs as rare, short, black prisms associated with quartz and centimeter-sized dark green tremolite.

Fluoro-potassichastingsite, KCa^sub 2^(Fe^sup 2^^sub 4^+Fe^sup 3^+)Si^sub 6^Al^sub 2^O^sub 22^Fa^sub 2^. I collected the first fluoro-potassichastingsite specimen from the dump of the Greenwood (Patterson) iron mine (type locality), located in the Hudson Highlands, Harriman State Park, Town of Tuxedo, Orange County. The mineral in the type material forms compact aggregates with crystals to 1 cm, associated with magnetite, diopside, enstatite, pyrrhotite, chalcopyrite, pyrite, and rarely phlogopite. It occurs as brittle, black, prismatic crystals, transparent and green in very thin fragments, with a greenish-gray streak and vitreous luster.

Fluorotremolite, Ca^sub 2^Mg^sub 5^Si^sub 8^O^sub 22^Fa^sub 2^, is an amphibole species that is not yet recognized by the IMA, but it falls in the new category of “named amphiboles,” which means that the mineral name can be used and published without prior approval if it is in accord with the amphibole nomenclature (Burke and Leake 2004). Petersen, Essene, and Peacor (1982) first described the mineral under the name “fluortremolite” in the Grenville Marble near Balmat, St. Lawrence County. Here, the fluorotremolite is “gemmy and colorless both in thin section and hand specimen.” The crystals are small (0.2-15 mm) with a fibrous habit and pale blue fluorescence in longwave and bright blue under shortwave ultraviolet radiation. Petersen et al. (1982) considered that the fluorescence is unrelated to the fluorine content but was present in those specimens with small amounts of iron.

I identified additional occurrences of fluorotremolite at the Redback iron mine and the Atlas quarry, Pine Island, both in Orange County. The fluorotremolite from the Redback mine occurs as a cluster of short prismatic, pale green crystals (5.86-5.90% FeO) developed in an olivine and pyroxene aggregate and does not show any fluorescence under longwave or shortwave ultraviolet radiation.

Fluorotremolite (fig. 8) from the Atlas quarry occurs in long prismatic to acicular, transparent, colorless to pale gray crystals to 4 cm, in parallel growth with fluoro-edenite, or isolated in marble. Inclusions of graphite flakes oriented along the elongation of the crystals are common. The mineral fluoresces pale yellow with a greenish tint in longwave and strong yellow with greenish tints in shortwave ultraviolet radiation.

Hastingsite, NaCa(Fe^sup 2^^sub 4^+Fe^sup 3^+)Si^sub 6^Al^sub 2^O^sub 22^OH^sub 2^, has an interesting history of its discovery and description. Early in the nineteenth century, Dr. Horton collected a mineral that was “black, often with brownish tarnish” from a quartz vein at Cornwall, Orange County. He gave it to Dr. Beck who described it in 1842 as “exhibiting one very perfect cleavage like some varieties of pyroxene.” Beck analyzed the mineral and wrote that “it resembles hornblende, or still more arfwedsonite [sic] in its appearance”; he considered the mineral as a new species and named it “hudsonite” in “allusion to the river in the vicinity of which it occurs.” Dana (1844) listed “hudsonite” as pyroxene with “no record of further examination of it” (Weidman 1903), a classification that was accepted by Beck (1850). Later, the mineral coming from the same material used by Beck was analyzed by Brewer in 1850 and by Smith and Brush in 1853 (in Weidman 1903). The later authors made a more complete analysis and found 1.95 percent water by ignition, indicating that the mineral was an amphibole and not a pyroxene. Unfortunately, neither chemical analyses nor optical properties were reported later. Adams and Harrington in 1896 described a similar mineral (Weidman 1903) and named it hastingsite, at Dungannon Township, in Hastings County, Ontario, Canada, and that became the type locality. Leake (1978) defined hastingsite as a valid species and recommended the name “hudsonite” no longer be used.

Hastingsite has been found in New York by many researchers as a common component of metamorphic rocks. At Carmel, Putnam County, it occurs as small, flattened, black prisms associated with epidote and dark green tremolite or as acicular crystals in calcite. I identified the mineral as black large prisms (to 5 cm) in anorthosite along the north-bound Interstate 87 between exits 30 and 31, as 2-3-cm-long black prisms associated with oligoclase in a narrow pegmatite dike cutting the anorthosite at Wadham, and associated with pyrrhotite at Lincoln Pond, all in Essex County; and as 2-cm-long prisms associated with plagioclase in the gabbro unit from the Rosetown pluton, Rockland County. Hastingsite has a significant amount of titanium in all of these locations (2.04-2.77 percent TiO^sub 2^), but the highest titanium content (up to 4.18 percent TiO^sub 2^) is shown by the specimens from the Rosetown pluton.

The iron deposits (the Hasenclever, Harris, Wilks, Daters, Cornell, and O’Neil mines) of the Hudson Highlands are also good places to collect hastingsite, even though the crystals are not very spectacular. In 2005, Michael Hawkins, my colleague from the New York State Museum, collected some beautiful small crystals (fig. 9) from an amphibole vein at the O’Neil mine, Orange County. In all these occurrences, hastingsite contains enough chlorine and/or fluorine and potassium to have been assigned the modifiers Cl-, F-, or K-rich.

Kaersutite, NaCa^sub 2^(Mg^sub 4^Ti)Si^sub 6^Al^sub 2^O23(OH)^sub 2^, is a major component of some igneous rocks. I identified it in the “cortlandtite” at Stony Point State Park in Rockland County, where it occurs in compact aggregates of short, black, prismatic crystals; I also identified it in two camptonite dikes, one at the Bradley mine and another in a road cut, both in Harriman State Park, Hudson Highlands, where it occurred as black prismatic phenocrysts to 1 cm long.

Magnesiohastingsite, NaCa^sub 2^(Mg^sub 4^Fe^sup 3^+)Si^sub 6^Al^sub 2^O^sub 22^(OH)^sub 2^, occurs as terminated and twinned, bladed, black crystals at Monroe (fig. 10) and in the iron deposits at the Wilks, Pine Swamp, Redback, and Boston mines, all in Orange County and at the Hasenclever mine in Rockland County. It contains potassium (0.34-0.42 apfu), fluorine (0.57 apfu at the Redback mine), and chlorine (0.45 apfu at the Hasenclever mine).

Magnesiohornblende, Ca^sub 2^[Mg^sub 4^(AlFe^sup 3^+)]Si^sub 7^AlO^sub 22^(OH)^sub 2^, was identified by me from three occurrences: the Phillips mine, Putnam County, as long prismatic, black crystals associated with pyrrhotite; as large, broken and cleaved, dark green crystals at the Beechy Bottom (Mica) mine, Rockland County; in a graphite- and phlogopite-bearing pegmatite, and as greenish- gray altered short prisms in a pegmatite from a road cut near Mineville, Essex County.

Pargasite, NaCa^sub 2^(Mg^sub 4^Al)^sub 5^(Si^sub 6^Al^sub 2^)^sub 8^O^sub 22^(OH)^sub 2^, occurs as stubby, black, terminated crystals (fig. 11) with a rusty coating at Warwick, as greenish bladed crystals at Edenville, both in Orange County, and at Edwards, St. Lawrence County, as large, black, almost tabular specimens. Pargasite also forms wide, dark rims enveloping almandine at the Barton mine garnet deposit, Warren County.

Potassicpargasite KCa^sub 2^(Mg^sub 4^Al)^sub 5^(Si^sub 6^Al^sub 2^)^sub 8^O^sub 22^(OH)^sub 2^, was identified by me as small, cleaved, shiny black crystals to 3 mm in association with magnetite, diopside, and hedenbergite at the Hogencamp and Surebridge iron mines in Orange County. A large specimen from Monroe, Orange County (fig. 12), is in the Union College’s mineral collection, Schenectady, New York. The latter is a fluorine-rich specimen, but the fluorine content is not enough to make it “fluoro- potassicpargasite.” Potassichastingsite, KCa^sub 2^(Fe^sup 2^^sub 4^+Fe^sup 3^+)Si^sub 6^Al^sub 2^O^sub 22^(OH)^sub 2^, like fluorotremolite, falls in the category of “named amphiboles,” and a formal description to recognize its species status is under way. Years ago, Michael Hawkins collected a specimen from the northwest wall of the cut at the O’Neil (Nail) mine, Orange County. Colony (1928) described it as glaucophane, saying that “almost pure glaucophane rock forms part of the northwest wall.” Potassichastingsite forms compact aggregates of up to 1-cm brittle, black crystals with a vitreous luster and a greenish-gray streak. It is associated with diopside, zircon, oligoclase, goethite, and albite in the holotype specimen.

Tremolite, Ca^sub 2^Mg^sub 5^Si^sub 8^O^sub 22^(OH)^sub 2^, occurs in many places in New York as colorless, pink or purple (“hexagonite”), bright green (chrome-tremolite), or dark green (actinolite) specimens, in different mineral associations and in varied environments.

The gemlike pink or purple tremolite is known to mineral collectors as “hexagonite” (fig. 13) and was collected first by John C. Trautwine from “near Edwards, St. Lawrence County” and presented by Goldsmith, 15 August 1876, in a paper to the Academy of Natural Sciences of Philadelphia, as a new mineral species: “anhydrous, and is crystallized in hexagonal form, it consequently belongs to the beryl group, of which it will be the third species.” It remained as a “new species” for only one month because Koenig (1876) determined that the mineral is monoclinic and the chemical composition differs from the composition of tremolite from Gouverneur, St. Lawrence County “by having replaced a small percentage of magnesium and calcium by manganese and sodium. The manganese produces the distinguishing color.”

The color of “hexagonite” is really due to the presence of manganese in the octahedral sites of the amphibole. Mn^sup 2^+ ions contribute to the pink and Mn^sup 2^+ cations to the violet color of the mineral (http://minerals.caltech.edu).

I analyzed many crystals from different sites around the Gouverneur area and found that the amount of manganese varies between 0.06 (Edwards) and 0.23 apfu (Wight mine) and the sodium content between 0.11 (Edwards) and 0.29 apfu (Wight mine). The mineral forms well-developed elongated blades or aggregates of very fine acicular crystals associated with blue diopside (“violan”), the manganese-rich OH-analogue of uvite, a friedelite-like mineral, talc, and quartz. It occurs as lenses or layers in the Mn-rich pods in the talc-tremolite schists of St. Lawrence County.

A bright green tremolite (“chromium tremolite”) occurs at the Gouverneur No. 1 Talc mine (American mine) in a manganese- rich pod from the talc-tremolite schists. Here, there are compact aggregates of small (to 5-mm), transparent, gemmy crystals associated with quartz, calcite, blue fluorapatite, and chromdravite. The chromium content is low (maximum 0.40 percent Cr^sub 2^O^sub 3^). The second occurrence for “chrome tremolite” is at the Alvin Washburn farm, St. Lawrence County. The crystals are short prismatic (fig. 14) to 2 cm, with a hexagonal cross section and a dark green color and are associated with calcite, albite, quartz, and uvite. They have approximately 0.39 percent Cr^sub 2^O^sub 3^ and 1.59-2.69 percent fluorine. The amphibole from both locations also contains some vanadium.

Colorless tremolite (fig. 15) is common, and at some locations gem-quality specimens have been collected. It occurs as bladed, prismatic, acicular, or fibrous crystals. The specimens from near the Seven Springs ski hill near Colton, St. Lawrence County, show twins parallel to {100} (fig. 16). Tremolite from the Calvin Mitchell farm, DeKalb, St. Lawrence County, forms fibrous aggregates in parallel growth with quartz (fig. 17). Spectacular aggregates of tremolite with an acicular habit (fig. 18) were found at Balmat. The “mountain leather” variety of tremolite was collected mainly at Lyon Mountain, Clinton County; St. Joe No. 3 mine and Gouverneur No. 1 Talc mine (American mine), both in St. Lawrence County; and in the No. 7 shaft at the Delaware aqueduct, where a “white to cream- colored lath-shaped sheet, 5 feet long, 4 inches wide and 0.5 inches thick” was noted (Zodac 1941).

The “colored” tremolite (actinolite) is also very common; the most important locations are listed by Robinson and Chamberlain (2007). The iron content varies from one location to another, and the color becomes darker with increasing iron content. The crystal habits include bladed, short or long, euhedral, prismatic (fig. 19), terminated crystals, as well as acicular, fibrous to asbestiform aggregates (Tilly Foster mine, Putnam County; GTC Wollastonite mine, Lewis County) or as curved fibrous crystals (Tilly Foster), in massive or spherulitic aggregates (Westchester County), and as single or groups of crystals in or on matrix.

Group Three: Sodic-Calcic Amphiboles

Two amphiboles from this group, fluororichterite and winchite, were identified and described from New York on two specimens from the New York State mineral collection. These sodic-calcic amphiboles have restricted occurrences and are common, especially in areas with extensive sodium metasomatism.

Fluororichterite, Na(CaNa)Mg^sub 5^Si^sub 8^O^sub 22^Fa^sub 2^ (fig. 20), is known from two occurrences in New York: at Natural Bridge, Lewis County, and Russell, St. Lawrence County. At Natural Bridge it occurs as short prismatic, white crystals to 1.5 cm that are similar to tremolite. Fluororichterite may form by metasomatic replacement of tremolite by the alkali- and halogen-rich hydrothermal fluids that pervasively invaded the region along the contact between Grenville marbles and the Diana Syenite. Another product of this alkali metasomatism in the Natural Bridge area is “gieseckite.” Unlike the Natural Bridge material, the fluororichterite from Russell forms dark greenish- black, prismatic crystals to 5 cm shortened along their c-axes and associated with corroded diopside and quartz. The specimen so described is in the A. E. Seaman Mineral Museum (DM 7899).

Winchite, (CaNa)Mg^sub 4^(Al,Fe^sup 3^+)Si^sub 8^O^sub 22^(OH)^sub 2^ (fig. 21), is known as a single specimen from Yonkers, Westchester County. It forms small fans of transparent, elongated, prismatic to acicular crystals.

Group Four: Na-Ca-Mg-Fe-Mn-Li Amphiboles

Two mineral species from this new group of amphiboles were described from their type locality in New York State: parvo-mangano- edenite and parvo-manganotremolite. They occur in a manganese-rich pod in the talc-tremolite schists hosted by the Grenville-age Upper Marble Formation, in St. Lawrence County.

Parvo-mangano-edenite, Na(CaMn)^sub 2^Mg^sub 5^(Si^sub 7^Al)8O^sub 22^(OH)^sub 2^, has a unique occurrence at the Arnold pit, near Fowler, St. Lawrence County, and was first identified and described by Benimoff et al. (1991) under the name “manganoan silicic edenite.” Further investigations (Oberti et al. 2006) showed that it is the new mineral species parvo-mangano-edenite. The crystals are small (0.2-0.5 mm), prismatic, elongated on [001], and have a vitreous luster and a brown-pinkish color. They are associated with parvo-manganotremolite, braunite, spessartine, talc, and very rare, tiny rhodonite grains. The optical properties of parvo-mangano-edenite and parvo-manganotremolite are similar, and even under the polarizing microscope they cannot be distinguished.

Parvo-manganotremolite, (CaMn)^sub 2^Mg^sub 5^Si^sub 8^O^sub 22^(OH)^sub 2^, a brown-pinkish mineral, has only one occurrence: the Arnold pit, St. Lawrence County. It was described by Oberti et al. (2006) as a new species adjacent to the rims of parvo-mangano- edenite or as tiny individual crystals associated with that mineral.

Discussion

The amphibole group in New York includes twenty-four known species that are named according to the rules established by the CNMNC of the IMA and includes representatives from four of the five known and recognized groups of amphiboles. By far, the most common are the calcic amphiboles; the sodic amphiboles have yet to be found in New York due to the lack of a suitable geological environment.

Five amphibole-species were first described and have their type locality in New York:

1. edenite (pre-IMA), Edenville, Orange County;

2. fluoropargasite (IMA 2003-050), Edenville, Orange County;

3. parvo-mangano-edenite (IMA 2003-062), Arnold pit, St. Lawrence County;

4. parvo-manganotremolite (IMA 2004-045), Arnold pit, St. Lawrence County;

5. fluoro-potassichastingsite (IMA 2005-006), Greenwood mine, Orange County.

Three of these amphiboles, parvo-mangano-edenite, parvo- manganotremolite from Arnold pit, St. Lawrence County, and fluoro- potassichastingsite from Greenwood mine, Orange County, have unique world occurrences in New York.

The geological environment controls the composition of the amphibole species and their distribution. The manganese-bearing lenses from the talc-tremolite schists in the marbles of St. Lawrence County contain specific mineral associations that may include cummingtonite, Mn-rich cummingtonite, lavender tremolite (“hexagonite”), parvo-mangano-edenite, and parvo-manganotremolite.

Both Grenville-age marble units from New York-Franklin (Orange County) and Upper Marble Formation (St. Lawrence County)-host fluoro- amphiboles. Other locations where the fluoro-amphiboles may be collected are some of the Precambrian iron deposits from the Hudson Highlands, in southern New York, and in the eastern and northeastern Adirondacks.

The potassichastingsite, potassicpargasite, chloro- potassichastingsite, and fluoro-potassichastingsite are found in the iron deposits from Hudson Highlands. Generally, the amphiboles from the iron deposits from both the Hudson Highlands and Adirondacks contain enough potassium, fluorine, and/or chlorine to have attached the K-, F-, or Cl- rich prefixes. Pargasite and hastingsite are common components of the metamorphic rocks of the Hudson Highlands and the Adirondacks, and tremolite, edenite, and pargasite are found in calcium-rich environments such as marbles or calc- silicate rocks.

Titanium-rich amphiboles such as kaersutite and Ti-rich hastingsite were described in igneous rocks and in pegmatite-like segregations in igneous rocks.

ACKNOWLEDGMENTS

I sincerely thank Dr. George Robinson, Dr. Steven Chamberlain, Dr. John Rakovan, and Michael Hawkins for their helpful discussions, suggestions, comments, and revisions that considerably improved the manuscript.

REFERENCES

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MARIAN LUPULESCU

3140 CEC

Research and Collections

New York State Museum

Albany, New York 12230

mlupules@mail.nysed.gov

Dr. Marian Lupulescu is curator of geology at the New York State Museum.

Copyright Heldref Publications May/Jun 2008

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