Here are the Answers:

A: Obsidian (Igneous)

B: Coal (Sedimentary)

C: Conglomerate (Sedimentary)

D: Granite (Igneous)

E: Sandstone (Sedimentary)

F: Quartzite (Metamorphic)

G: Shale (Sedimentary)

H: Slate (Metamorphic)

I: Mica Schist (Metamorphic)

J: Basalt (Igneous)

K: Gneiss (Metamorphic)

L: Limestone (Sedimentary)

M: Marble (Metamorphic)

N: Pumice (Igneous)

O: Scoria (Igneous)