Megacrystic potassium feldspar gneiss

Title

Megacrystic potassium feldspar gneiss

Identifier

AD-5

Description

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 represent a metamorphosed igneous plutonic rock. Similar lithologies are present at other stratigraphic horizons in the Adirondacks. In the Northwest Adirondack Lowlands, Buddington referred to a similar lithology as the Hermon Granite Gneiss. The present samples would be more appropriately referred to as metamorphosed quartz-monzonites. Sporadic occurrences of orthopyroxene indicate that, locally at least, the lithologies are charnockitic.
Thin section shows plagioclase, quartz, hornblende and orthopyroxene.

Date

1980

Contributor

Western Minerals Inc.

Spatial Coverage

Adirondack Highlands-collected from a road cut 2.25 miles north of Hamilton-Fulton counties line at sharp curve on NY Route 10, approximately 5.5 miles north of Junction wjth Route 29A.

Temporal Coverage

Precambrian

Accrual Method

Purchased from Western Minerals Inc.

Unit

Rooster Hill Formation

Number of Thin Sections

1

Geolocation