6.24: Chert
- Page ID
- 89752
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El chert es una roca sedimentaria silícea de grano fino. Es un duro, denso, y consiste principalmente en cristales microscópicos entrelazados de cuarzo y puede contener ópalo. Tiene una fractura concoidal y puede ocurrir en una variedad de colores. La mayoría de las formas de cerda a partir de la recristalización de restos de microplancton silíceo (el exudado silíceo finalmente pierde su contenido de agua, recristaliza y se convierte en chert.
Los residuos orgánicos conservados como camas de cerda se conocen a partir de rocas que datan de la época precámbrica temprana. Las formaciones de hierro bandeado (BIF) están compuestas por capas intercaladas de minerales de óxido de hierro y cerdo, y se cree que son de origen biológico. Los querts marinos más jóvenes se forman principalmente a partir de diatomeas y exudados radiolarios.
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| Figura 6.85. Capas de cerda marina expuestas en Marin Headlands, California | Figura 6.86. Formación de hierro bandeado (con cerda) de la era precámbrica. |