aa is a form of lava flow associated with Hawaiian-type volcanoes, consisting of basaltic rock, usually dark-colored with a jagged and loose, clinkery surface.
2 is CASH, "A name applied by Europeans to various coins of low value in the East Indies and China: esp. a. The basis of the monetary system which prevailed in Southern India up to 1818; in this system 80 cash = 1 fanam, 42 fanams = 1 star pagoda (about 7s. 8d.)."