Sand and gravel deposits found on beaches or in rivers and streams, are mostly quartz (silicon dioxide, SiO2) grains. Weathering of rocks such as granite forms these quartz grains. In the process of weathering, the softer, weaker minerals in granite (such as feldspar) are weathered away. The more resistant quartz eventually is ground down in size, but does not break down chemically. In time, these quartz grains accumulate in rivers, streams, deltas and on beaches.
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Explanation:
Sand and Gravel
Sand and gravel deposits found on beaches or in rivers and streams, are mostly quartz (silicon dioxide, SiO2) grains. Weathering of rocks such as granite forms these quartz grains. In the process of weathering, the softer, weaker minerals in granite (such as feldspar) are weathered away. The more resistant quartz eventually is ground down in size, but does not break down chemically. In time, these quartz grains accumulate in rivers, streams, deltas and on beaches.