is about 80 miles (130 km) long in the north-south direction and about 25 miles (40 km) wide east to west. Even more of it remains hidden underground. Geologists have found the granite at the bottom of deep wells on the plains and magnetic sensors have detected it as much as to the east. Mineralogy The granite ranges in color from light pink to almost red. The pink color is due to large amounts of microcline feldspar and various iron minerals that permeate the rock. The long cooling time and the chemical composition of the original magma allowed large crystals to precipitate out of the magma. As a result, in many places the granite is very coarse grained, made up almost entirely of large crystals of feldspar, typically about a centimeter across. This makes the granite easily weathered and very crumbly. Almost every hill and slope in the Pikes Peak region is covered with thick blankets of loose gravel (scree) made up of marble-sized grains of feldspar. In some places, the cooling process lasted long enough to form pegmatites that contain large, pure crystals of various minerals. The chemistry of the cooling magma produced a complex and unique mineralogy that attracts collectors from around the world and the Pikes Peak region is famous for its spectacular mineral specimens. Smoky quartz crystals and topaz are found in many places in the Pikes Peak granite. Probably the most famous mineral from the area is amazonite, a bluish form of microcline feldspar that is relatively rare in other parts of the world. Many museum collections have stunning specimens of deep blue amazonite crystals studded with jet-black smoky quartz crystals. See also References Further reading 1. Granite Tectonics Of Pikes Peak Composite Batholith Colorado Pegmatite Symposium - 1986 R.M. Hutchinson - Colorado School of Mines 2. Colorado Gem Trails and Mineral Guide Richard M. Pearl 3rd rev. ed. 1993 3. Geology of the Rocky Mountains Geologic formations of Colorado Pikes Peak