Every inch of granite represents roughly 100,000 years of slow crystal growth deep within the Earth.

Granite is an intrusive igneous rock that forms from the slow crystallization of magma below the Earth's surface. Unlike volcanic basalt, which solidifies in days, granite plutons can take up to 1 million years to fully crystallize. This extremely slow cooling rate allows the characteristic large mineral grains of quartz, mica, and feldspar to develop.Geologists at institutions like the British Geological Survey note that granite typically forms at depths of 2.4 to 48 kilometers beneath the crust. At these depths, the surrounding rock acts as an insulator, trapping heat and slowing the cooling process dramatically. Research suggests that a single inch of granite represents approximately 100,000 years of thermal history.The specific texture of granite is known as phaneritic, meaning the crystals are large enough to be seen with the naked eye. Crystal size is directly proportional to cooling time. If the magma had reached the surface and cooled rapidly, it would have formed a fine-grained rock like rhyolite instead.Radioisotopic dating of zircon crystals found within granite allows scientists to determine the precise age of these formations. Many of the granite batholiths visible today, such as those in Yosemite National Park, are over 100 million years old. These massive stone structures were eventually exposed at the surface through tectonic uplift and erosion.