Which of the following is an extended definition of aa?
Aa is not an abbreviation; it is a noun that refers to a particular kind of igneous rock with a rough surface texture.
An iron-rich lava forming irregular, broken rocks is called aa.
Aa lavas harden into jagged rocks, unlike pahoehoe lavas, which form smooth surfaces.
Hawaiian lava flows that solidify into sharp, jagged rock are called "aa." I always remember the name by imagining that trying to walk over these rough surfaces made ancient Hawaiians yell "ah! ah!" in pain.