It is an essential part of most mobile gadgets sold around the world and demand for cobalt is soaring. But the process of extracting the mineral from the earth comes at a huge human cost. A Sky News investigation has found children as young as four working in dangerous and squalid conditions in Cobalt mines in the Democratic Republic of the Congo for as little as 8p a day. Sky's special correspondent Alex Crawford reports. SUBSCRIBE to our YouTube channel for more videos: http://www.youtube.com/skynews Follow us on Twitter: https://twitter.com/skynews and https://twitter.com/skynewsbreak Like us on Facebook: https://www.facebook.com/skynews For more content go to http://news.sky.com and download our apps: iPad https://itunes.apple.com/gb/app/Sky-News-for-iPad/id422583124 iPhone https://itunes.apple.com/gb/app/sky-news/id316391924?mt=8 Android https://play.google.com/store/apps/details?id=com.bskyb.skynews.android&hl=en_GB