A meteor hunter has stumbled on two marble-sized nuggets of an asteriod that detonated after colliding with the Earth, worth 10 times as much as gold, according to scientists.

The tiny stones were found in northern California's Sierra foothills, part of the asteroid that exploded with a third of the force of Hiroshima atomic bomb, scientists say.

The rocks each weigh about 10 grams, said John Wasson, professor and expert in meteorites at University of California Los Angeles Institute of Geophysics and Planetary Physics.

Talking of his discovery, Robert Ward of Prescott, Arizona, said he "instantly knew" he'd found a rare meteorite known as 'CM' - carbonaceous chondrite - based in part on the "fusion crusts from atmospheric entry" on one side of the rock.

He has two rocks that he suspects were part of the same small meteorite that split on impact, reported the Daily Mail.

Ward said the discovery was a "thrilling moment". "It is one of the oldest things known to man and one of the rarest types of meteorites there is. It contains amino acids and organic compounds that are extremely important to science," he added.

Experts say the rock fragments come from a flaming meteor which dates from the early formation of the solar system around four to five billion years ago.