Both minute textural details and the overall petrographic features of volcanic rocks are markedly clarified through the examination of etched, polished thin sections by using the reflected-light differential interference contrast (DIC) apparatus of G. Nomarski. The sensible two-dimensional nature of the stage object (relief ≤0.5 μm) permits precise definition of the forms of the crystalline and noncrystalline components of the rock and therefore defines their precise spatial relations. The Nomarski DIC techniques, which can readily be combined with traditional polarized transmitted-light microscopy, should prove particularly effective in the study of rocks containing abundant dark glass.

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