Which is older gneiss or granite

Gneiss is an old German word meaning bright or sparkling. Other specimens - Click the thumbnails to enlarge. Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks. After metamorphism, the schist is very foliated the minerals of the rock are arranged in layers. It can be easily split into thin, flakey pieces. Schists often have a high luster they are very shiny due to large crystals within the rock.

Department of Earth, Atmospheric, and Planetary Sciences. Photo courtesy of Arizona Tile. Gneiss, arguably, is more visually interesting. The stone captures the expressiveness and movement that come from its dynamic origins. The striped, wavy look of gneiss comes from extreme amounts of compression.

The random orientation of minerals you see in granite is an inefficient use of space, sort of like the ragtag pile of magazines you left next to the couch. Those magazines take up less space if you stack them all the same way, right? This principle applies to minerals too. They align themselves in the same direction when they get buried a few miles deep and pressed between colliding continents. If the pressure on the stone is evenly distributed, you get straight or gently flowing stripes, like Agatha Black or Viscount White.

If the compression involves folding or twisting, as it often does in geologic crumple zones, then you get a stone with wavy or ribbonlike texture. Amadeus and Black Forest are examples of gneisses with dynamic textures. The parent rock of gneiss can be granite, but it can also be shale or an impure sandstone meaning it contains more than just pure quartz sand. Previous articles have described the continuum of metamorphism as a stone is exposed to increasingly torturous heating and compression.

Shale becomes slate , then phyllite, then schist, then gneiss. Each of these steps is gradual, as the stone slowly changes in response to the conditions it experiences.

Photo courteys of M S International. Regardless of its geologic parent rock, gneiss is near the end of the metamorphic road.

Heat it further and it begins to melt. The mineral quartz will melt first. Another delicious food analogy applies here.

The beginning of the melting process is just like a chocolate chip cookie left in a warm car. The chocolate chips will melt long before the rest of the cookie does.

In gneiss, you can often see fluid-looking pockets of quartz that were melted while the rest of the rock remained solid.