The oldest rock in the world is not from Earth because it is a moon rock. Moon rocks are mostly anorthosites.
An anorthosite is an igneous rock that is mainly composed of plagioclase feldspar (rock-forming aluminum). These rocks are found on both the Earth and the moon.
Some scientists believe that the anorthosites on the moon formed when feldspar crystallized and became part of a global magma ocean that surrounded the moon after it formed.
Currently, one of the oldest rocks on Earth may be the Lunar Sample 67215. This rock sample was picked up from the moon during the Apollo 16 mission. It is also an anorthosite and it is believed to be about 4.46 billion years old.
Lunar Sample 67215 was collected from the rim of North Ray Crater on the moon. Analysis of the rock revealed that it came from the shallow layer of the moon's crust. Thus, the rock may provide information on how the lunar crust was formed.
Anorthosite rocks from the moon have mostly been dated to be about 4 billion years old and some of them even contain traces of water.
Another moon rock that is just as old Lunar Sample 67215 was collected from the moon by Apollo 14 astronauts. The rock came to be known as "Big Bertha." This rock was also dated to be about 4 billion years old. Big Bertha is actually an Earth rock that was found on the Moon meaning that it originated from the Earth itself and not the moon.