One of the most challenging mining projects in the world was Mirny diamond mine in Russia. The development started in 1957, in extremely harsh climate conditions. During the 7 month-long winter engineers found that steel tools became so brittle that they broke like match sticks, oil froze into solid blocks, rubber tires shattered like fragile crockery, and in summer the top layer of permafrost melted into a swamp of uncontrollable mud. Despite this, engineers turned Mirny into an open-pit mine. At its operational peak the mine produced over 10 million carats of diamonds per year.