6. Well-rounded grains in a clastic sedimentary rock indicate

a. the absence of cleavage in the mineral clasts.

b. rapid transport and deposition.

c. numerous collisions between particles during extensive transportation.

d. lack of chemical weathering.

c. numerous collisions between particles during extensive transportation.

Explanation:

The shape of the sandy grains can also contribute to deciphering the history of a sandstone. When water currents, wind or waves move sand and other sedimentary clasts, the grains lose angled edges and corners and become more rounded as they collide with other particles during transport. Therefore, it is likely that rounded grains have been transported by air or water. In addition, the degree of roundness indicates the distance or time spent in transporting the sediment by air or water currents. Very rounded grains indicate that there has been great abrasion and, consequently, prolonged transport.

Very angular grains, on the other hand, mean two things: that the materials underwent transportation for a short distance before their deposit, and that they may have been transported by some other means. For example, when glaciers move sediments, clasts usually become more irregular due to the crushing and grinding of ice.

In addition to affecting the degree of roundness and the degree of selection that the clasts experience, the duration of transport through turbulent water and air currents also influences the mineral composition of a sedimentary deposit. Substantial weathering and prolonged transport lead to the gradual destruction of weaker and less stable minerals, including feldspars and ferromagenesians. Since quartz is very durable, it is usually the mineral that survives long excursions in a turbulent environment.