(ADK) Anorthosite-Charnockite and Metamorphic Suite --
Adirondack Mountains, New York


(ADK) Anorthosite-Charnockite and Metamorphic Suite --
Adirondack Mountains, New York


The Adirondack Mountains of northern New York State are underlain by approximately 20,000 square miles of complexly deformed, high grade metamorphic rocks which are believed to represent a southern outlier of the much larger Grenville Province.The Adirondacks can be divided into the "Lowlands" and the "Highlands" . The Lowlands comprise the northwestern quarter of the belt and are characterized by amphibolite facies metamorphism. The Highlands appear to consist entirely of granulite facies rocks. All rocks in this suite have been collected from the Highlands and predominantly from the southern quarter of the Adirondacks.

This suite of rocks is designed to be representative of the Highlands in general. Therefore it includes both metasedimentary and metaigneous rocks. The latter are very common throughout the Adirondacks and contain the often-discussed anorthosite-charnockite suite of rocks. Almost all rocks in the Adirondack Highlands are strongly foliated. This is the result of intense polyphase deformation that has affected this area.




Western Minerals Inc.

Spatial Coverage

This rock suite was collected from the Adirondack Mountains located in the northeastern part of New York State.

Temporal Coverage

The Adirondack Mountains were formed approximately 1.1- 1.3 billion years ago during the Grenville Orogeny (Precambrian eon, Proterozic era).

Accrual Method

Purchased from Western Minerals Inc.


Start here: 
McLelland, J., and Selleck, B.W.,2011, Megacrystic Gore Mountain-type garnets in the Adirondack Highlands; age, origin, and tectonic implications:Geosphere, v.7, no. 5, p.1194-1208, doi: 10.1130/GES00683.1.
  • This article describes the formation of the megacrystic garnet amphibolites in the Gore Mountain section of the Adirondack Mountains. The authors conclude that three main factors influenced the garnet development: collapse of the Ottawan orogeny, intrusion of Lyon Mountain Granite, and fluid-related alteration at high temperature.

Additional resources:
McLelland, J.M., Bickford, M.E., Hill, B.M., Clechenko, C.C., Valley, J.W., and Hamilton, M.A., 2004, Direct dating of Adirondack Massif anorthosite by U-Pb SHRIMP analysis of igneous zircon; implications for AMCG complexes: Geological Society of America Bulletin, v.116, no. 11-12, p.1299-1317, doi: 10.1130/B25482.1.

  • This article describes techniques used to more accurately date the Adirondack Massif anorthosite.The authors concluded that the massifs constitute a single, composite anorthosite-mangerite-charnockite-granite (AMCG) suite intruded at ca. 1155 Ma. Although the rock suite is considered to be coeval, the authors conclude the rocks are not comagmatic.

McLelland, J., Bickford, M.E., Spear, F., and Storm, L., 2002, Geology and geochronolgy of the eastern Adirondacks in New England Intercollegiate Geological Conference, 94th, New York State Geological Association 74th: guidebook for field trips in New York and Vermont : Lake George, New York

  • This field trip guide provides for nine stops in the eastern Adirondacks. It also include some thin sections images and zircon images from sample rocks of the field trip stops.

McLelland, J., Daly, J.S., and McLelland, J.M., 1996, The Grenville orogenic cycle (ca. 1350-1000 Ma); an Adirondack perspective: Tectonophysics, v.265, issue 1-2, p.1-28, doi: 10.1016/S0040-1951(96)00144-8.

  • This article provides a detailed geochronological account of the Grenville orogeny (ca. 1350-1000 Ma) with emphasis on the impact it had on the formation of the Adirondack Mountains.

McLelland, J., Lewis, A., and Moore, L., 1994, Composition and petrogenesis of oxide-, apatite-rich gabbronorites associated with Proterozoic anorthosite massifs: examples from the Adirondack Mountains, New York: Contributions to Mineralogy and Petrology, v.116, p.225-238, doi: 10.1007/BF00310702.

  • This article investigates the occurence of oxide-, apatite-rich gabbronorites with anorthosite massifs of the Adirondacks. The authors describe a multilple-step process of plagioclase crystal fractionation that ultimately leads to high concentrations of P, Fe, and Ti.

New York State Geological Survey

  • The NYS Geological Survey is a division of the New York State Museum system. This web page provides some details about the Adirondack Highlands and pictures of various minerals found in this region.

Regan, S.P., Chiarenzelli, J.R., McLelland, J.M., and Cousens, B. L., 2011, Evidence for an enriched asthenospheric source for coronitic metagabbros in the Adirondack Highlands: Geosphere, v.7, issue 3, p. 694-709, doi: 10.1130/GES00629.1.

  • This article describes the formation of coronitc metagabbros through tectonic processes involving the asthenosphere. Through geochemical and isotopic analyses, the authors provide a timeline of tectonic and petrologic events that supports an asthenospheric source for coronitic metagabbros.

Collection Items

OCR PDF of supplemental information for the Anorthosite-Charnockite Metamorphic Suite-Adirondack Mountains, New York collection.

This specimen is typical of the 5-10 foot thick coarse grained layers of glassy quartzites that comprise this formation. In most instances the quartzites are about 90% quartz. Feldspar and garnet are encountered locally. This is presumed to be the…

This charnockite is similiar to most of the Adirondack charnockites that occur interlayered with other metastratified units. Like its analogues, the Canada Lake charnockite shows conformable realationships with enveloping units. Mineralogically,…

Pyroxene-quartz-plagioclase gneiss
This specimen consists of 50-60% andesine, 20-30% quartz, and minor pyroxene and hornblende. Associated with this lithology are 2-6 inch layers of pyroxene-plagioclase granulite and amphibolite. It is believed that the Royal Mountain Member gneiss…

Sillimanite-garnet-biotite-quartz-plagioclase gneiss
The predominant lithology of the Peck Lake Formation is a sillimanite-garnet-biotite-quartz-oligoclase gneiss with pods and lenses consisting of two feldspars and quartz (anatectic?). The lithology is widespread throughout the Adirondacks and may…

Megacrystic potassium feldspar gneiss
This lithology is characterized by 1-4 inch long megacrysts of microperthite in a groundmass of quartz, oligoclase, hornblende, orthopyroxene, garnet, and oxide. Although the contacts of this unit are everywhere conformable, the rock is believed to…

Orthopyroxene gabbro
This specimen is typical of the saturated gabbros of the Adirondacks. The plagioclases are generally in the range of Anâ‚„â‚€ and the orthopyroxenes average close to En₆₀. Antiperthite is locally developed. Scattered grains of ilmenite and garnet…

This calcite marble is typical of most Adirondack metacarbonates. In the majority of instances, original dolomite has reacted to yield calcsilicates. Also present in these specimens are small, serpentinized droplets which may originally have been…

Calcsilicate rock
Minerals found in the calcsilicate facies contain quartz, diopside, enstatitic pyroxene, tremolite, calcite, and phlogopite. However, only a few thin sections have been found to contain all phases. In some specimens, the pyroxene is close to 100%…

Pods and lenses of green diopsidite commonly occur along with the marbles. They are often composed of over 90% diopside.
Thin section contains diopside.

Garnetiferous amphibolite
This specimen is similar to the famous garnet deposits at Barton Mines at Gore Mountain. The garnets at Gore Mountain can attain diameters of 3 feet. At the Speculator road cut, garnet of 8-10 inches in diameter have been found, but smaller examples…

Sillimanite-garnet-quartz-feldspar gneiss
This specimen is extremely rich in sillimanite. European geologists refer to such lithologies as "khondolites." This locality is very near some of the old graphite production sites west of Hague.
Thin section shows sillimanite, garnet, k-feldspar.

Two-pyroxene-plagioclase granulite
The Sacandaga Formation consists of a well layered series of dark granulites (AD-12) and leucogneisses (AD-13). Orthopyroxene is generally present in greater quantity than clinopyroxene. It is not known whether these rocks are metasedimentary or…

Garnetiferous leucogneiss
This rock type is characteristic of the light colored layers in the Sacandaga Formation. The mineralogy consists of garnet, feldspar, and quartz. Occasionally, sillimanite and skeletal oxides occur. Both plagioclase and microcline are present. Quartz…

Tennantville gabbroic anorthosite
This medium grained facies is one of a number of anorthositic sheets that intrude throughout the stratigraphic section of the southern Adirondacks. A chemical analyses of specimens from this outcrop yield results that are almost identical with…

Quartz-microcline-diopsite gneiss
This specimen displays an unusual and distinctive lithology that occurs primarily in lower, marble-rich units (for example, the Cedar River Formation).
Thin section shows quartz, K-feldspar and clinopyroxene.

Garnetiferous olivine metagabbro
This specimen is typical of the olivine metagabbros that occur throughout the Adirondacks. These rocks are of great petrologic interest for they contain classic examples of garnet coronas and spinel-clouded plagioclase. Note the preservation of…

The specimen was collected from the Oregon Dome Massif. The Oregon Dome is similar in all respects to the anorthosites described and analyzed by Buddington (1939) for the Adirondack High Peaks region (Marcy Massif). Texturally, the present specimens…

Coarse anorthosite
This coarse-grained specimen is typical of the massive, homogeneous anorthosite that occurs within the Marcy Massif and underlies the High Peaks region of the Adirondacks. The anorthosite from Route 3 is best represented by analyses 5-L and 8, Table…

Two Pyroxene-spinel metagabbro
The locality near Northville, NY represents the only example of this assemblage that has been encountered to date (1980) in the Adirondacks. The original lithology is that of a typical olivine metagabbro. During granulite facies metamorphism,…
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