Inside the carbon crystal is an imperfection - a deposit of minerals jam-packed with hydroxl ions, that almost always come from water.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/evidence-water-found-third-way-earths-core
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/sydney-morning-herald
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/science-and-technology
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-resources