Chert is a sedimentary rock made almost entirely of quartz crystals. In the Great Lakes region of North America, chert forms as veins in limestone or as layers between other sedimentary rocks. Chert is very hard, so any fossils that formed in or of chert may be less eroded than those softer rock, like limestone.
In 2012, Hurricane Sandy kicked up 20+–foot waves on Lake Michigan’s Left Coast and scattered rocks by the millions onto beaches. Among those were deeply caramel-colored, jagged chunks of chert.
Chert delivered onto Lake Michigan beaches by Hurricane Sandy, Autumn 2012, by Left Coast Creative (© 2017 Elizabeth G Fagan) for the blog Lake Michigan’s Left Coast