Deep in the heart of the Omani desert, the search is on for rocks worth millions of dollars: not diamonds but rubble that has fallen from the sky.br br A group of German and Swiss scientists are working with the Omani government to catalogue the vast number of meteorites that lay strewn across the desert - famed as the place with the world's second largest cache of heavenly rocks.br br Al Jazeera's Andrew Hopkins reports from Oman.