The three principle classes of rocks are igneous, metamorphic, and sedimentary. Granophyre is an example of an igneous rock, formed by the cooling and solidification of magma from the Earth’s crust.

Granophyre is similar to, but more fine textured than, granite. The material often occurs in layered intrusions among other rocks, such as gabbro. Porphyritic, granophyre is characterized by the presence of large, distinct crystals in a finely grained groundmass. The crystals and groundmass are both primarily quartz and alkali feldspar.

The age of rocks can be estimated through the use of radiometric dating, a measurement of the decay of long-lived radioactive isotopes of elements that occur naturally in rocks and minerals. In Western Australia, zircon crystals in some sedimentary rocks have been found to be approximately 4.3 billion years old, which makes them oldest known material on the planet. However, the Earth is believed to be even older than the crystals since the planet’s rocks have been destroyed and then recycled through plate tectonics.