Gneiss is a metamorphic rock composed of bands and lenses of various minerals, according to Geology.com. "Our candidates for the oldest U.S. rock are ancient gneisses with complex histories.

Michigan, Minnesota and Wisconsin all feature ancient rocks known as gneisses — metamorphic rocks banded with various minerals — but an analysis determined that the gneiss in northern Michigan ...

Abstract U‐Pb zircon data on gneisses indicate a Late Proterozoic protolith at ∼700 Ma at Bixiling and a Late Archean to Early Proterozoic for the Shuanghe sheet within the ultrahigh‐pressure ...

Abstract Mineral inclusions in zircon from gneisses in the ultrahigh‐pressure (UHP) zone of the Dabie Mountains, China, are studied by using laser Raman spectrophotometry. We identified numerous ...

Frost agrees. The 3.8-billion-year-old zircons in the Michigan and Wyoming gneisses hint at older rocks that were either recycled in Earth’s mantle or remain buried in the crust.