Forged in the very severe temperatures and pressures of the mantle of the Earth, diamonds at their basic most form are compressed carbon crystals. While diamonds may seem simple to the eye, the diamond formation process is extremely complex. As a new study shows, the origin tale of some diamonds involves a surprising bit player: the sea.
As geochemist named Yaakov Weiss and his teammates show in a recent study, diamonds from the Northwest Territories of Canada owe their existence in the Earth to a very old ocean. Seawater from about 200 million years before got stuck in a huge slab of the Pacific Ocean crust, forced below the North American Plate. The ocean water-laced crust moved deeper to the inside of the Earth, ultimately reaching the mantle lots of kilometers underneath the surface. The seawater reacted with mantle rocks, and it changed these rocks’ chemical composition, which allowed diamonds to grow.
Prior to this study, geologists knew the formation of diamond depended on some form of liquid. Where that liquid came from and what it was, were the open questions. This recent proof that it is ancient seawater came from analyzing a special kind of diamond known as “fibrous diamond”.
Beyond just carbon formation, some diamonds are pricier than others. While some loose diamonds are radiant and beautiful and shine with fire, others are drab and cloudy, full of fluid flaws which take away their luster.
Fibrous diamonds have no real value or use to jewelers, but these are invaluable to scientists. Yaakov Weiss says, “What those fibrous diamonds give you are the fluids—in their original form—that [reacted and] changed the chemistry of the deep lithosphere.”
Fibrous diamonds grow more quickly as compared to the monocrystalline type – the colorless and clear gemstones familiar to most individuals. For this reason, fibrous diamonds capture millions of small samples of the rocks and fluids which existed about them when they formed.
By studying the liquid trapped inside 11 fibrous diamonds taken from diamond deposits in the Territories, Yaakov Weiss and his mates found chemical evidence that connects the fluid to old seawater.
Based on further analyses of West African diamonds, Weiss suspects that these lackluster stones from across the world formed from the same process. Even monocrystalline diamonds of jewelers may owe their life to sub-ducted seawater, he says.
Weiss plans to examine more of these dull gems from other parts of the world to check if it is possible for him to obtain any other information about the geological processes taking place deep inside the Earth.