Granite

Granite is the most familiar of all intrusive igneous rocks — coarse-grained, hard, durable, and the foundation rock of most continental crust. The name covers a broad family of rocks rich in feldspar, quartz, and small amounts of mica or amphibole. The characteristic salt-and-pepper appearance comes from the contrast between light-colored feldspar and quartz crystals and darker mafic minerals scattered throughout.

Granite forms when molten magma cools slowly deep underground — often miles below the surface — over thousands to millions of years. The slow cooling allows individual mineral crystals to grow large enough to see with the naked eye, distinguishing granite from chemically similar but fine-grained volcanic rocks like rhyolite (essentially extrusive granite that cooled too fast for crystals to grow).

The exposed granite of mountain ranges like the Sierra Nevada, the White Mountains of New Hampshire, Mount Rushmore in the Black Dakotas, and Half Dome and El Capitan in Yosemite cooled in massive batholiths 80-100+ million years ago and was subsequently exhumed by tectonic uplift and erosion of overlying rocks. The rounded "exfoliation" sheets of these granite domes form as the rock expands upward when overlying pressure is removed, cracking off in concentric layers like the layers of an onion.

Granite is the dominant building stone of monumental architecture. The pyramids of Egypt include granite components shipped from Aswan; the U.S. Capitol, the Lincoln Memorial, the New York Stock Exchange building, and countless courthouses and banks are clad in granite for its combination of beauty, durability, and association with permanence. Granite countertops became a dominant high-end kitchen finish in the late 20th century and remain widely popular.

The species "granite" is geologically diverse — Vermont and New Hampshire produce gray granite; Texas red granite (used in the Texas State Capitol) is famous for its color; Brazilian and African ornamental granites supply much of the modern countertop market. Granite is the state rock of New Hampshire ("The Granite State"), Vermont, North Carolina, South Dakota, Idaho, and Wisconsin.