A MASSIVE DIAMOND of 404.2 carats (almost 1/5 lb.) made the December 16, 2016, cover of Science, the weekly magazine of the American Association for the Advancement of Science. It’s quite the rock, and Science gives newly discovered details of its origin. These get technical pretty quickly, which got me refreshing my memory bank about such precious gems. And, wouldn’t you know, I gleaned enough stuff to warrant two items here at SimanaitisSays.
Today, the Science aspects. Tomorrow, tidbits of massive diamonds, which, I admit, sounds oxymoronic.
This 404.2-carat rough diamond, 2 3/4 inches tall, was recovered from the LuLo Mine, Angola, in February 2016. This and other images from Science, both print and online.
The word diamond comes from the Greek, ἀδάμας – adámas, “unbreakable.” However, diamonds aren’t exactly “forever.” Chemically, they’re a metastable form of carbon, the metastable moniker implying that their “diamond lattice” crystal structure is less stable than graphite’s. Rest easy, though, because in ordinary conditions the conversion from diamond to graphite is negligibly slow.
Natural diamonds are formed in the Earth’s mantle at extremes of heat and pressure. The mantle is immediately beneath the Earth’s paper-thin outmost layer of about 3 to 30 miles down. And, indeed, “paper-thin” is a good analogy: On an eight-inch globe, the crust would have the thickness of a sheet of paper.
The mantle, about 1800 miles thick, makes up almost 7/8 of the Earth’s volume. It’s semi-solid with metallic liquids under great pressure and high temperature. This latest research posits that certain diamonds, the Type II variety, arise in these metal-saturated regions of the mantle.
Type II diamonds are those with no measurable nitrogen impurities; they make up less than two percent of natural diamonds. They’re typically large, relatively pure and irregularly shaped.
A Type II diamond leaves geologic clues of its origins in those specific impurities it possesses.
Evan Smith of the Gemological Institute of America and his colleagues from the U.S., Italy and South Africa examined 53 Type II diamonds. For 38 of these diamonds, the only inclusions were of a magnetic, metallic character. One conjecture of this finding is that such diamonds form within the mantle at depths of 255 to 570 miles. Another suggests how these massive gems are formed.
A model of such diamond formation.
The researchers say that in the mantle a liquid metal composition evolves of Iron, Nickel, Carbon and Sulfur. The carbon crystalizes within these metallic liquid pockets. These diamonds then physically separate from their growth environment and work their way to the crust through volcanic action.
This complex path leads from the Earth’s mantle to what Science magazine calls “A Geologist’s Best Friend.”
Tomorrow, I describe the goings-on of several of these massive diamonds. Involved, in one manner or another, are various European royalty, a thief or two, F. Scott Fitzgerald and Mickey Mouse. ds