At 4 billion years old, this gneiss is the oldest known rock that formed on Earth. The Earth is about 500 million years older still, but little record of that early time has survived our planet's geologic activity.
The iridescent blue quartz in this folded rock formed under high temperatures produced by a continental collision 1.1 billion years ago. During a later collision, the rock was incorporated into the Appalachian Mountains.
The white bands in this 3.96-billion-year-old gneiss consist of quartz and feldspar, two minerals common in granite. Their presence tells us the gneiss was metamorphosed from granitic rock contained in Earth's earliest continental crust.
This 1.7 billion-year-old gneiss is part of a 500-km (300-mi) wide area that accreted to North America’s southern margin. Once sedimentary, the rock was metamorphosed and folded. It contains layers and veins of granite.
This gneiss from near Denver, Colorado, formed deep in Earth's crust 1.7 billion years ago. Stress and high temperatures reorganized its minerals into alternating pink and dark gray layers. Notice the very thin pink-and-white vein that cuts across the layers.
Gneiss is a Metamorphic rock--one that was transformed from older rocks by heat and pressure within the Earth. Two continents collided 1.7 billion years ago, burying and heating a sandstone. Its minerals recrystallized and separated into alternating layers. Molten granite invaded this gneiss, forming a vein that was later deformed into a zigzag shape.
This gneiss was caught in a deep, hot part of a fault zone between rocks moving in opposite directions. The movement stretched the mineral grains into long ribbons. You can see the grains that form the ribbons by viewing the end of the rock.
About 2.6 billion years ago, a granite crystallized deep in the crust. Later, it was metamorphosed into this gneiss. The collision of the Wyoming Province and North American craton 1.8 billion years ago folded the layers of the gneiss.