These metamorphic rocks are garnet gneiss. The garnet fragments are the round dark brown mineral in the rocks. The rocks measure around 12 cm x 10 cm x 6 cm in size or less. Number of objects in this ...

Oldest North Cascades bedrock, a 400-million-year-old tale from European origins.

Under more intense conditions gneiss was metamorphosed into amphibolite. Gneiss and amphibolite contain dark layers or crystals of hornblende, a mineral that’s calcium-iron-magnesium-potassium rich.

Morton gneiss (pronounced “nice”), named for the town in Renville County where it has been quarried, is one of the oldest stones on the planet: about 3.5 billion years old.

But the Acasta Gneiss is the oldest intact piece of Earth’s crust, according to Elizabeth Cottrell, chair of the department of mineral sciences at the National Museum of Natural History.

The Acasta Gneiss outcrop in Northern Canada is generally regarded as the oldest known intact crustal fragment on Earth. The minerals at the site are unique due to the high content of silica they ...