In the XIX century, Rene Haüy named “amphibole” meaning “ambiguous” a group of minerals that show the same appearance but very different chemical composition. We know at this moment that the amphiboles contain more than 100 species; they have a complicated structure characterized by numerous crystallographic sites and very complex composition. Amphiboles are important mineral constituents of the metamorphic and igneous rocks and some ore deposits. They were found also in meteorites.
The general chemical formula of the amphibole-group is written as
A = Na, K, Ca, Li
B = Na, Li, Ca, Mn2+, Fe2+, Mg
C = Mg, Fe2+, Mn2+, Al, Fe3+, Mn3+, Ti4+, Li
T = Si, Al, Ti4+
W = (OH), F, Cl, O2-
The amphiboles are divided into 5 groups based on the crystal site occupancy:
Group 1: Mg-Fe-Mn-Li amphiboles;
Group 2: Calcic amphiboles;
Group 3: Sodic-calcic amphiboles;
Group 4: Sodic amphiboles;
Group 5: Na-Ca-Mg-Fe-Mn-Li amphiboles.
The amphiboles in New York include 24 known species that are named according to the rules established by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) and have representatives from four of the five known and recognized groups of amphiboles. These are:
Group 1: anthophyllite, cummingtonite, anganocummingtonite;
Group 2: actinolite, chloro-potassichastingsite, edenite, ferro-actinolite, ferro-edenite, ferropargasite, fluoro-edenite, fluoropargasite, fluoro-potassichastingsite, fluorotremolite, hastingsite, kaersutite, magnesiohastingsite, magnesiohornblede, pargasite, potassicpargasite, potassichastingsite, tremolite;
Group 3: fluororichterite, winchite;
Group 5: parvo-mangano-edenite, parvo-mangano-tremolite.
Five amphibole-species were first described and have the type locality in New York:
- Edenite (pre-IMA), Edenville, Orange County;
- Fluoropargasite (IMA 2003-050), Edenville, Orange County;
- Parvo-mangano-edenite (IMA 2003-062), Arnold Pit, St. Lawrence County;
- Parvo-manganotremolite (IMA 2004-045), Arnold Pit, St. Lawrence County;
- Fluoro-potassichastingsite (IMA 2005-006), Greenwood Mine, Orange County.
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 cummingtonite, manganocummingtonite, lavander tremolite (“hexagonite”), parvo-mangano-edenite and parvo-manganotremolite;
- The Grenville-age marble units from New York, Franklin (Orange County) and Upper Marble Formation (St. Lawrence County) host fluoro-amphiboles.
- The iron deposits from Hudson Highlands contain potassichastingsite, potassicpargasite, chloro-potassichastingsite and fluoro-potassichastingsite.
- The marbles or calc-silicate rocks of the Hudson Highlands and the Adirondacks contain pargasite, hastingsite, tremolite, and edenite;
- Titanium-rich amphiboles such as kaersutite and Ti-rich hastingsite were described in igneous rocks and in pegmatite-like segregations in igneous rocks.
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Amphiboles first found in New York
Lupulescu, M. V., J. Rakovan, G. W. Robinson, and J. M. Hughes. 2005.Fluoropargasite, a
new member of the calcic amphiboles from Edenville, Orange County, New York. The Canadian Mineralogist. 43, p. 1423-1428.
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edenite, parvo-mangano-tremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles. American Mineralogist, 91, p. 526-532.
Lupulescu, M. V., J. Rakovan, M. D. Dyar, G. W. Robinson, and J. M. Hughes. 2009. Fluoro-potassichastingsite from the Greenwood Mine, Orange County, New York: a new end-member calcic amphibole. The Canadian Mineralogist, v 47, p. 909-916.
Lupulescu, M. 2008. Amphibole-group minerals from New York State. Rocks & Minerals, v. 83, No 3, p. 210-219.