Bulletin . (A) Outcroj) of Virgilina j-Tcenstone, North Fork of Aarons Creek, live miles nortliof (B) Typical outcrop of Virgilina greenstone three miles northwest of Viro-ilina. VIRGILIXA GREENSTONE 29 The color of the porphyritic and the amygdaloidal rocks varies greatly,but is usually a kind of grayish-green, the intensity of the color dependingupon the relative amounts of chlorite, epidote, and hornblende in the areas have a purplish-gray color, but this is not nearly so pronouncedas with the tufPaceous rock, which is occasionally of a decidedly purplecolor. Many spec
Bulletin . (A) Outcroj) of Virgilina j-Tcenstone, North Fork of Aarons Creek, live miles nortliof (B) Typical outcrop of Virgilina greenstone three miles northwest of Viro-ilina. VIRGILIXA GREENSTONE 29 The color of the porphyritic and the amygdaloidal rocks varies greatly,but is usually a kind of grayish-green, the intensity of the color dependingupon the relative amounts of chlorite, epidote, and hornblende in the areas have a purplish-gray color, but this is not nearly so pronouncedas with the tufPaceous rock, which is occasionally of a decidedly purplecolor. Many specimens of the rock, when viewed on a cleavage surface,present a kind of pearly lustre or sheen, which is probably due to thedevelopment of sericite or some other micaceous mineral in the planes ofschistosity. It is also not usually possible from the examination of such asurface to distinguish the porphyritic rock from certain phases of themashed tuff. The determinative characteristics of the porphyritic rockconsist of phenocrjsts of plagioclase feldspar which can be seen to goodadvantage only when the roc
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