7.4.1: Common Minerals

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The previous chapter discussed silicate minerals common in igneous rocks. In principle, they could all be detrital grains in sediments and sedimentary rocks. In practice, most break down so quickly that they cannot be weathered or transported very much before completely decomposing. Quartz is the most resistant to weathering. It is also a common component of many igneous and metamorphic rocks found at the Earth’s surface. Many minerals weather to produce clays. It is no surprise, therefore, that quartz and clays are the main silicate minerals in most clastic rocks. Feldspars and sometimes muscovite may also be present but are usually subordinate to quartz. They are absent from rocks formed from sediments transported long distances or weathered for long times. Mafic silicate minerals are exceptionally rare in sediments or sedimentary rocks. Besides quartz and clays, other silicates, including zeolites, may occasionally be present. Important non-silicate minerals in clastic rocks include carbonates, sulfates, oxides, halide minerals and occasionally pyrite.