Riolita.docx - 1 Riolita Concepto La riolita es una roca...

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1 Riolita Concepto. La riolita es una roca ígnea extrusiva, volcánica félsica, de color gris a rojizo con una textura de granos finos o a veces también vidrio y una composición química muy parecida a la del granito. A la riolita se le considera el equivalente volcánico del granito, lo que se agrega a otras evidencias que demuestran que el granito se origina a partir de magma, tal como lo hace la riolita, solo que a mayor presión. La textura afanítica de la riolita hace que se vea muy diferente al granito a pesar de sus similitudes. Su textura se debe al corto periodo de cristalización, lo que obstaculiza la formación de grandes fenocristales y favorece la formación de vidrio. Tiene una alto contenido en SiO 2 oxido de silicio (superior al 65%). Está compuesta por cuarzo, sanidina y plagioclasa, y biotita y magnetita como minerales accesorios. Si se incrementa la presencia de plagioclasas la roca pasa a ser una dacita.
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