Most natural diamonds have ages between 1billion and 3.5billion years. Most were formed at depths between 150 and 250 kilometers (93 and 155mi) in the Earth's mantle, although a few have come from as deep as 800 kilometers (500mi). Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds. Much more recently (tens to hundreds of million years ago), they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites.