X1011576476-00226-55848</DOCNO> Obsidian Rocks Obsidian Rocks Obsidian rocks are igneous rocks that form when lava cools quickly above ground.
(Obsidian Rocks Obsidian Rocks Obsidian rocks; are; igneous rocks that form) (igneous rocks; form; T:when lava cools quickly above ground) (lava; cools quickly; L:above ground)
Obsidian Rocks Obsidian Rocks Obsidian rocks igneous rocks lava
are form cools quickly
igneous rocks that form
T:when lava cools quickly above ground
L:above ground