Abstract

The genesis of some pyroxenes and garnets related to Adirondack anorthosite, anortho-site-marble contact zones and their metamorphic equivalent are discussed on the basis of 10 clinopyroxenes whose chemical analyses as related to optical properties have recently been presented by Hess, and upon one new orthopyroxene analysis and 7 new garnet analyses given here. It is found that the clinopyroxenes of the anorthositic rocks are high in alumina as compared with those of gabbro. In contact zones with marble, ferrosalite and grossularite-andradite skarn is developed on the marble side whereas an almandite-rich mafic gneiss is often found as a border facies on the anorthositic side. One sheet of salite gabbro is interpreted as the product of assimilation of ferrosalite skarn by gabbroic anorthosite magma.

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