True icebergs are galcier fragments that have fallen into the sea. Glaciers are made of compacted smow, which is fresh water. Additionally, “sea ice” that forms from the freezing of sea water is also basically fresh water as well. This is because when saltwater freezes, it excludes salt from the ice crystal lattice.
Most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers (87 to 118 mi) in the Earth’s mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth).