Here are the Answers:

A: Conglomerate (Sedimentary)

B: Scoria (Igneous)

C: Basalt (Igneous)

D: Shale (Sedimentary)

E: Slate (Metamorphic)

F: Sandstone (Sedimentary)

G: Coal (Sedimentary)

H: Granite (Igneous)

I: Gneiss (Metamorphic)

J: Limestone (Sedimentary)

K: Marble (Metamorphic)

L: Obsidian (Igneous)

M: Quartzite (Metamorphic)

N: Mica Schist (Metamorphic)

O: Pumice (Igneous)