Gneiss is a type of rock that is formed from other rocks through intense heat and pressure. It has distinct layers or bands, making it look striped or banded.
Full definition
The samples
of gneiss were collected by the American geologist Samuel Bowring at Washington University in St Louis.
«The oldest rocks in the Koongarra area, domes of granitoids and
granitic gneiss, are of Archaean age (ie to geologists this means they are older than 2500 million years).
The orange rock in the foreground is Webb
Canyon gneiss, granite formed by decompression melting more than 2.6 billion years ago.
Petrogenesis, detrital zircon SHRIMP U-Pb geochronology, and tectonic implications of the Upper Paleoproterozoic Seosan iron formation, western Gyeonggi SHRIMP U — Pb zircon dating of the Neoproterozoic Penglai Group and
Archean gneisses from the Jiaobei Terrane, North China, and their tectonic implications
Large flake graphite showings located on the property were confirmed with flake size in the range of 0.5 to 2 millimeters, typically present in shear zones at the contact
of gneisses and marbles where the graphite content usually ranges from 2 % to 20 %.
CT likened it to a metamorphic rock, maybe not marble but it was certainly very «
gneiss», he quipped.
These types of rock — including limestone and
gneiss — are gradually broken down into sand which, unlike gravel and pebbles, is dispersed widely as it travels downstream.
Named the Tava sandstone, this sedimentary rock forms intrusions within the ancient granites and
gneisses that form the backbone of the Front Range.
Measurements on some 50 grains of zircon from
the gneiss rocks found in Canada showed them to be 3.962 billion years old, with a margin of error of only three million years.
Simba Kopje is one of the many Kopjes in this landscape, displaying a number of
gneiss and granite outcroppings, a result of volcanic activities.