Coccolithophores are microscopic algae that first appeared 220 million years ago, and flourished during the cretaceous period. They produce peculiar plates called cocoliths out of calcium carbonate, and incorporate them into an external shell. They constantly remove carbon from the atmosphere as they die and sink to the ocean floor, producing chalk. This is an important feedback system in the global carbon cycle.
Well, this blog is called “Star in the Stone” and that’s exactly what a pallasite is! How beautiful to reveal translucent gemstones welded into a molten mass. Peridot crystals can only be formed in outer space, brought down to earth in meteors.
There are three main types of meteorites. Those made entirely of iron alloy, are thought to be the cores of asteroids that melted early in their history. They consist mainly of iron-nickel metal with small amounts of sulphide and carbide minerals. Iridium, is brittle, with a high melting point, similar to silver or platinum, an element very rare on earth, but often found in meteors. Most iron meteorites have a distinctive crystalline structure with bands containing low and high levels of nickel, known as Widmanstatten texture, which is highlighted when acid-etched. Second, there are those meteorites made of an iron-stone blend, called pallasites. These consist of almost equal amounts of iron-nickel metal and silicate minerals, and are amongst the most beautiful of meteorites, because of the gemstones they contain. Pallasites contain big, beautiful olive-green crystals, a form of magnesium-iron silicate called olivine, embedded entirely in metal. Pallasites can show big variations. Sometimes the olivine does not occur as a single crystal but as a cluster and elsewhere it can create a pattern of veins through solid metal.
Third, are the stoney concretions, or chondrites, which consist mainly of silicate materials, such as olivine or feldspar, in conglomeration with iron or carbon. They are the most primitive meteorites in their chemical development. Chondrites come from asteroids that did not melt when formed. Carbonaceous chondrites often contain water-bearing minerals and compounds including the organic molecules such as amino acids, the building blocks of life on earth. Chondrites are the materials from which the solar system formed and have been little changed compared with rocks from the larger planets, which have been subjected to billions of years of geological activity. They are very similar in composition to the sun and can tell us a lot about how the solar system itself was formed. A variant of chondrite, called Achondrites include meteorites from asteroids, Mars and the moon. They are igneous, meaning that at some point they melted into magma. When the magma cools and crystallises, it creates a concentric layered structure, usually with metallic center and silicon coated exterior. This process is known as igneous differentiation,
which gave rocky planets of Mercury, Venus, Earth and Mars them planetary crusts, mantles and cores. Achondrites can, therefore, tell us a lot about the internal structure and formation of the planets.
Apparently this is old news now. However, I just recently heard of it, and find it fascinating. Here is the story of the largest known diamond in our galaxy.
On Friday, 13th February, 2004, the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, who study the origin, evolution and ultimate fate of the universe, released information about their latest discovery – a10 billion trillion trillion carat diamond.
The newly discovered cosmic diamond is a chunk of crystallized carbon, the size of our Moon, 50 light-years from the Earth in the constellation Centaurus. It is 4000kms wide and weighs 5 million trillion trillion pounds or 10 billion trillion trillion carats.
“You would need a jeweller’s loupe the size of the Sun to grade this diamond!” says astronomer Travis Metcalfe who leads the team of researchers that discovered the giant gem. The diamond has been called ‘Lucy’ – a tribute to the Beatles song ‘Lucy In The Sky With Diamonds’, Technically known as BPM 37093, this huge cosmic gem, is actually a crystallized white dwarf. A white dwarf is the hot core of a star, left over after the star uses up its nuclear fuel and dies. It is made mostly of carbon and is coated by a thin layer of hydrogen and helium gases.
The white dwarf is not only radiant but also harmonious. It rings like a gigantic gong, undergoing constant pulsations. For more than four decades, astronomers have thought that the interiors of white dwarfs crystallized, but obtaining direct evidence became possible only recently. “The hunt for the crystal core of this white dwarf has been like the search for the Lost Dutchman’s Mine. It was thought to exist for decades, but only now has it been located,” says co-researcher Michael Montgomery.
The problem with proving the theory about the crystallization is that by the time the star has crystallized, it is no longer pulsating and is so cool, that they are impossible to detect. But BPM 37093 is so massive, that the star is crystallizing on the inside, as white light and sound continue to pulsate from the surface. The vibrations are detectable as colour shifts in the visible light emanating from the star. In this case, the right frequency makes it a diamond – blue green in tint.
“By measuring those pulsations, we were able to study the hidden interior of the white dwarf, just like seismograph measurements of earthquakes allow geologists to study the interior of the Earth. We figured out that the carbon interior of this white dwarf has solidified to form the galaxy’s largest diamond,” says Metcalfe.
Scientist Vince Ford, of the Australian National University’s Mount Stromio Observatory, said “This huge …..thing is sitting right down in the southern sky, in the constellation of Centaurus, just near the Southern Cross”. At approximately 4000kms in diameter, Lucy is roughly the same size as Australia and completely outclasses the largest diamond on Earth, the 530-carat Star of Africa that resides in the Crown Jewels of England. The Star of Africa was cut from the largest diamond ever found on Earth, a 3,100-carat gem.
Our Sun will also become a white dwarf when it dies 5 billion years from now. Some two billion years after that, the Sun’s ember core will crystallize as well, leaving a giant diamond in the centre of our solar system. The Sun is part of a group of stars called main sequence stars and most of these end their lives as white dwarves.
Sirius B, which is a known white Dwarf star, will also be a diamond in the future. Sirius B is currently around 25,000 degrees on the surface, and will begin to crystallize when it has cooled to about half that temperature.
It’s interesting to me, to imagine the possibility of somehow capturing this dead star and bringing it back to earth, where we value diamond as a rare commodity. Yet considering it’s great size, such an object brought to earth, would depreciate itself by its veritable massiveness. Scarcity is what increases value. A diamond the size of Australia, if it were suddenly available, would be about as worthless as the sand beneath our feet. Perhaps this is why the Aztecs couldn’t understand when the Spanish Conquistadors suddenly began to attack them for the gold adornments decorating their architecture and selves. Gold, readily available in South America, had no appreciable value for the local tribes in the sense it did as a rarity in Europe. One man’s trash is another man’s treasure. And vice versa, one man’s treasure is another man’s trash.
Coccolithophores are microscopic algae that first appeared 220 million years ago, and flourished during the cretaceous period. They produce peculiar plates called cocoliths out of calcium carbonate, and incorporate them into 
an external shell. They constantly remove carbon from the atmosphere as they die and sink to the ocean floor, producing chalk. This is an important feedback system in the global carbon cycle.
Star in the Stone 