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23.0 Porphyritic trachyte. Devils Tower, Wyoming. Large white to clear phenocrysts of alkali feldspar (anorthoclase) and small phenocrysts of clinopyroxene (augite and aegirine) crowd the aphanitic matrix. [Scale shows cm divisions.]
Image 52 of 156
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![23.0 Porphyritic trachyte. Devils Tower, Wyoming. Large white to clear phenocrysts of alkali feldspar (anorthoclase) and small phenocrysts of clinopyroxene (augite and aegirine) crowd the aphanitic matrix. [Scale shows cm divisions.]](../23.0.JPG)