On each of the three sides, they will discuss a rock type (igneous, sedimentary, metamorphic) with one or two sentences and a picture.
(they; will discuss; a rock type (igneous, sedimentary, metamorphic; with one or two sentences and a picture; L:On each of the three sides)
they
will discuss
a rock type (igneous, sedimentary, metamorphic with one or two sentences and a picture L:On each of the three sides