Question

insert one comma to separate the coordinate adjectives. volcanic ash, which has an abrasive sandy texture, can include various identifiable particles: crystals, minerals, bits of pumice, shards of volcanic glass, and miscellaneous rock fragments.

Explanation:

Coordinate adjectives modify a noun equally and can be separated by a comma. "Abrasive" and "sandy" both modify "texture" and are coordinate adjectives.

Answer:

Volcanic ash, which has an abrasive, sandy texture, can include various identifiable particles: crystals, minerals, bits of pumice, shards of volcanic glass, and miscellaneous rock fragments.