What size of rock is referred to as cobble?

The term "cobble" is used in geology to refer to a specific size category of rock. Cobble is defined as rock fragments that range in size from approximately 64 millimeters (about 2.5 inches) to 256 millimeters (about 10 inches) in diameter. This size range places cobble between boulders, which are larger, and gravel, which is smaller.

Understanding these size classifications is crucial in fields such as erosion and sediment control, as the size of materials can influence their behavior in soil and water management practices. For example, larger materials like cobbles and boulders tend to have different erosion and transport characteristics compared to smaller gravel or silt particles.

In summary, the correct answer reflects the accurate size relationship among different types of rock materials, with cobble being larger than gravel but smaller than boulders.