In pictures: Nigeria's stone crushers

The enterprising stone crushers surrounding Nigeria’s capital, Abuja, can be considered the new agents of weathering, reports the BBC News website's Senan Murray.

They spend their days breaking down hard granite to sell to builders - achieving in hours what would take nature centuries.

But the work is really hard and fraught with health hazards.

It is their cheap rocks that feed the voracious construction industry in central Nigeria's fast-growing urban areas.