Garnetiferous amphibolite

Garnetiferous amphibolite

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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 were considered to be best suited for the purposes of this suite. Both at Gore Mountain and Speculator, the original rock can be shown to have been an olivine metagabbro. The present mineralogy consists of garnet, hornblende, and plagioclase with the development of narrow rims of very anorthitic plagioclase (An₈₀) surrounding many of the garnets. In addition, orthopyroxene locally replaces hornblende near the plagioclase rims.

The following information is from the original OCR document: The origin of the garnetiferous amphibolites has been discussed by Bartholome, "Genesis of the Gore Mountain Garnet Deposit", 1960, Economic Geology, v. 55, p. 255-277. The rims of calcic plagioclase and associated orthopyroxene has been discussed by deWaard, "The Occurrence of Garnet in the Granulite Facies of the Adirondack Highlands, " 1965, Journal of Petrology, v.6, p. 165-191. DeWaard shows convincingly that these rims are formed during the reaction hornblende + garnet + quartz = orthopyroxene + plagioclase + Hâ‚‚O.

Thin section shows plagioclase, hornblende and garnet.

1980

Western Minerals Inc.

Adirondack Highlands-collected on NY Route 30 from a road cut 0.9 miles north of Speculator, NY.

Precambrian

Purchased from Western Minerals Inc.

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