Pegmatite

Pegmatite intrusions along the Painted Wall

NPS Photo

Pegmatite refers to igneous rock showing very coarse texture with unusually large, intergrown crystals. It consists mostly of quartz, feldspar, and mica. As magma cools and solidifies, water becomes concentrated. This concentration makes the magma more fluid and easier to squeeze, like toothpaste out of the tube, into the surrounding rock. The crystals can be very large—up to 6 feet (2 m) in length.

Pegmatite is abundant throughout Black Canyon. It is found in the form of large bodies, stripes, and "dikes." Since it is more resistant to erosion, it sticks out boldly against less resistant gneiss and schist. There were three episodes of pegmatite intrusion in the Black Canyon rocks. The most spectacular example of these intrusions is the Painted Wall, the tallest cliff in Colorado standing 2,250 feet (686 m). Other large bodies or outcroppings of pegmatite can be found upstream from East Portal or at Kneeling Camel on the north rim of Black Canyon.

 

Microcline

Microcline comes from the Greek words "micros" or small, and "klinein," to incline. This silica-rich (SiO2) member of the feldspar family is enriched in potassium (K) and can be white, or pink with hints of yellow. Mircrocline is a hard mineral that breaks at right angles. The feldspar within the pegmatite here is mostly a pink microline.

Like some of the other common minerals, this one is found in many places in both the metamorphic and igneous rocks.