Question

Rocks have two distinct grain size.​

Answer 1

Explanation:

Bimodal" grain-size distribution means two distinct grain-size populations. In a porphyritic andesite, for instance, 75% of the volume of the rock may be aphanitic (<1/16 mm) and the remaining 25% of the volume may be represented by a population of larger (~8 mm) crystals (e.g., hornblende, plagioclase).

Answer 2

Explanation:

Bimodal" grain-size distribution means two distinct grain-size populations. In a porphyritic andesite, for instance, 75% of the volume of the rock may be aphanitic (<1/16 mm) and the remaining 25% of the volume may be represented by a population of larger (~8 mm) crystals (e.g., hornblende, plagioclase).