What Diamond is to kimberlite and Lamproite

Diamond is....
... to Kimberlite & Lamproite

The complex volcanic magmas that solidify into kimberlite and lamproite are not the source of diamonds, only the elevators that bring them with other minerals and mantle rocks to Earth's surface.

Although rising from much greater depths than other magmas, these pipes and volcanic cones are relatively small and rare, but they erupt in extraordinary supersonic explosions.

Kimberlite and lamproite are similar mixtures of rock material. Their important constituents include fragments of rock from Earth's mantle, large crystals, and the crystallized magma that glues the mixture together.

The magmas are very rich in magnesium and volatile compounds such as water and carbon dioxide. As the volatiles dissolved in the magma change to gas near Earth's surface, explosive eruptions create the characteristic carrot- or bowl-shaped pipes.

Kimberlite magma rises through Earth's crust in networks of cracks or dikes. The pipes only form near Earth's surface. This cross-section of a kimberlite pipe shows the carrot-shaped profile produced by explosive eruption.

The root zone starts in fissures, where gases are released from the rising magma and drive the eruption; they blow out the fragment-laden kimberlite to form the volcano's tuff ring and fill the pipe. Depth measurements show the level of erosion for various kimberlite pipes in South Africa. Adapted from Hawthorne (1975).

These drawings illustrate the formation and filling of the typical champagne-glass shape of a lamproite pipe.

The initial stage of the eruption, powered by gases either from the lamproite magma or from boiling ground water, corrodes the hosting rock to form the champagne-glass shape (top).

The eruption then produces particles of ash, lapilli, and pumice that partially fill the crater and form a tuff ring (middle).

Finally, the crater fills with a lava pond from the degassed lamproite magma (bottom).

Adapted from a sketch by Barbara Scott-Smith..

Diamonds as Mineral Indicators

Diamonds as...
... Indicators.

Certain minerals are present in the rocks from the upper mantle that occur with diamonds in kimberlite and lamproite pipes, as seen in nearby cases of xenoliths and diamond inclusions. Some of these minerals, being resistant to weathering and denser than quartz sand, concentrate in channel bottoms.

Because they occur in far greater abundance than diamond, exploration geologists look for these "indicators" among the gravel of regions they suspect may host diamond-bearing pipes.

Indicator minerals for diamond include, in order of decreasing significance: garnet, chromite, ilmenite, clinopyroxene, olivine, and zircon. But the order of persistence in streams is zircon, ilmenite, chromite, garnet, chromian diopside, and olivine.

Diamond itself is obviously a most important indicator.

Most indicator minerals have a distinctive color. Seen here are red pyrope garnets, green chromian clinopyroxene, black ilmenite and chromite, and yellowish-green olivine...

Where on Earth Diamonds can be found.

Where Diamonds...

.... can be found on Earth

The search for diamonds has determined that most are derived from kimberlite pipes in the oldest, nuclear portions of the continents, where the basement rocks are older than 1.5 billion years.

The oldest parts of continents are called cratons, and can be divided into two terranes: Archean-age archons, which are older than 2,500 million years, and Proterozoic-age protons, which are 1,600 -- 2,500 million years old. The distribution of these terranes is shown on the map. Kimberlite pipes occur in many parts of the continental crust, but most diamond-rich ones are found in archons.

This fact suggests that most diamonds were formed and stored deep below the cratons, in the area shown in the lower figure, and were later transported to the surface by kimberlite and lamproite magmas that extracted them and other samples from the mantle.

Diamond surf to the surface

How Diamonds Move....

..... to the Surface of Earth

Diamonds ascend to the Earth's surface in rare molten rock, or magma, that originates at great depths. Carrying diamonds and other samples from Earth's mantle, this magma rises and erupts in small but violent volcanoes. Just beneath such volcanoes is a carrot-shaped "pipe" filled with volcanic rock, mantle fragments, and some embedded diamonds.

The rock is called after the city of kimberlite, Kimberley, South Africa, where the pipes were first discovered in the 1870s. Another rock that provides diamonds is lamproite.

The volcano that carries diamond to the surface emanates from deep cracks and fissures called dikes. It develops its carrot shape near the surface, when gases separate from the magma, perhaps accompanied by the boiling of ground water, and a violent supersonic eruption follows. The volcanic cone formed above the kimberlite pipe is very small in comparison with volcanoes like Mount St. Helens, but the magma originates at depths at least 3 times as great.

These deep roots enable kimberlite to tap the source of diamonds. Magmas are the elevators that bring diamonds to Earth's surface.

100 Million Years Ago

Sections of the Earth's Interior (center to surface):
Inner Core, Outer Core, Lower Mantle, Upper Mantle, Crust

Diamonds are Formed in the Upper Mantle
Kimberlite magma rings move up from the Mantle
Diamonds are carried upward by the magma
Magma and gases explode to the surface
Falling ash and rocks form a cinder cone

Millions of Years Later
Only a slight depression remains

Today
A South African Diamond Mine

Formation..

Formation....

....Of the Diamond

Experiments and the high density of diamonds tell us that they crystallize at very high pressures. In nature this means that diamonds are created by geologic processes at great depth within Earth, generally more than 150 kilometers down, in a region beneath the crust known as the mantle. Other processes, explored later in this exhibition, bring diamonds to where people can find them.

This diagram shows the interior structure of Earth. The three concentric layers -- the core, mantle, and crust -- formed within a few hundred million years of Earth's coalescence 4.5 billion years ago. The core is primarily an iron-nickel alloy and makes up a large fraction of the mass of Earth. The vast mantle is sandwiched between the core and the thin crust and is composed predominantly of magnesium and iron silicate minerals. Our planet's crust is a thin, rocky skin. Diamonds can form in most of Earth's interior but not near its surface, where graphite is the stable form of carbon. Indeed, diamonds only survive at Earth's surface because great heat is required to break down the diamond structure.

The upper mantle is slightly plastic, which allows it to circulate slowly in a creeping, convective flow that helps drive the surface motion of Earth known as "plate tectonics."

The cross section shown here provides a closer look at Earth's crust and underlying mantle. The crust can be divided into ocean basins, underlain by a thin layer of dense, basaltic rock, and continents, formed of a much thicker but less-dense layer of granitic rocks. Just below the crust is the portion of the mantle called the lithosphere, which is rigid and acts like rock. Below this is the asthenosphere, a more plastic, flowing region that enables the overlying crustal plates to move in what is known as plate tectonics.

The plot of pressure and temperature shows the conditions at which either diamond or graphite exist. The general conditions present in the Earth are described by curved lines called geotherms. Note that there are two geotherms: Because the continental crust is old and thick, conditions are somewhat colder in and beneath it than beneath the much younger ocean basins.

Diamonds can form at depths as shallow as 150 kilometers beneath the continental crust, while beneath oceans they need depths of at least 200 kilometers, as shown by the diamond boundary on the cross-section.

Origin Of Diamonds..

Diamond is carbon...

.....Where does this come from.

Most diamonds consist of primeval carbon from Earth's mantle, but those from eclogites probably contain carbon recycled from the ocean crust by plate tectonics -- the carbon of microorganisms. How do we know?

Carbon atoms occur in three different masses, or isotopes. Unlike high-temperature processes in deep Earth, low- temperature, biological processes, such as photosynthesis, are sensitive to the differences in mass, and actively sort different carbon isotopes. Thus, the ratios of carbon isotopes in organic materials -- plants, animals, and shells -- vary, and also differ from those in the carbon dioxide of the atmosphere and the oceans. Geochemists "read" the carbon isotopes in samples to interpret nature's record.

Virtually all carbon atoms, the ones in a diamond or a tree or you, came from the stars. Particularly at Earth's surface the proportions of 12C and 13C (the carbon isotopes of mass 12 and 13) get redistributed. Expressed as simple numbers in 13C notation -- in which larger numbers mean more 13C -- organic carbon has large negative values, average Earth has a mildly negative value, and the carbon in shells is near zero.

The narrow range of 13C values for harzburgitic diamonds in the histogram on the top resembles the range of average Earth, indicating that the mantle is the likely carbon source. The large range for eclogites suggests mixing of organic carbon (the strongly negative numbers), mantle carbon (mildly negative numbers), and shell-like carbon (values near zero). These data support recycling of once-living carbon from Earth's surface deep into the mantle to form diamond.

When ocean floor slides into the mantle, the basaltic rock becomes eclogite, and organic carbon in sediments may become diamond

What is Diamond..

Journey ....
.... into Diamonds


DIAMOND. The mere mention of the word fills the mind with a multitude of concepts and images. Diamond is a mineral, a natural crystalline substance, the transparent form of pure carbon. Diamond is something superb, the peerless "king of gems" that glitters, dazzles, and symbolizes purity and strength. Diamond is for engagement and the 75th wedding anniversary, for a commitment to never-ending love. Diamond is indomitable, the hardest surface known. Diamond is exotic, formed in Earth's interior and shot to the surface by extraordinary volcanoes. A diamond is likely the oldest thing you will ever own, probably 3 billion years in age, fully two thirds the age of the Earth. Diamond is a strategic and high-tech supermaterial for our technological society. Diamond is a shape. This exhibition presents the fascinating story of the nature of diamonds.

DIAMONDS....

...... are FOREVER




There are no maps or directions on the journey of LOVE...
It's about each step you take together and moments you
realize your love has grown and deepened.
Journey of diamonds, a series of stones set in
varrious sizes, shapes and cuts symbolises
the journey......of Diamonds.

The Four C's

Color Diamond color is graded on a scale of the alphabet, using letters D through Z. The letters A, B, and C aren't used. This is because when the Gemological Institute of America invented the scale they wanted to disassociate it from jewelry stores that used their own color grade scales. The colors D, E, and F are considered to be completely colorless. D is of course, the best. Some famous diamonds are actually leaning towards the Z end of the scale but aren't quite "Fancy colored", like the faint yellow 55-carat Sancy Diamond. The largest known D-color diamond in the world is the Centenary, which weighs 273.85 carats. The second largest is probably the Millennium Star, which weighs 203.04 carats. Some diamonds do not fit onto the scale, such as fancy colored diamonds. Diamonds occur in every color of the rainbow. The rarest colors are red and purple, and combinations of those two colors. Yellow and brown are the most common color of diamond, but colorless is the most popular as far as jewelry is concerned. (Colored diamonds are very gradually appearing in more and more jewelry stores as they become more well-known.) Blues and greens are very rare, especially naturally colored stones. Some lightly colored diamonds (light light pink, light light blue, ect.) are irradiated to make their color more intense. This means that low fields of radiation are beamed into the cut and polished stone, darkening the outer part of the stone all the way around. The process is permanent and professionally accepted in the diamond industry. Probably the largest irradiated diamond is the Deepdene, a 104.88-carat golden yellow cushion shaped stone.

This is the color scale for brown diamonds with no secondary colors.

There are essentially 7 degrees of color intensity for brown.
The color scale for colorless to near-colorless diamonds.

A natural fancy colored diamond will cost you much much more than an irradiated one. Such well known diamonds as the Hope, the Dresden Green, the Tiffany Yellow, the Conde Pink, and Sultan of Morocco, the Transvaal Blue, the Wittelsbach, the Agra, and the Great Chrysanthemum are all very very unique because they were not irradiated. One remarkable stone, the Dresden Green, stands out amoung the naturals. It is the largest green diamond in the world at 40.70 carats. The fact it is an historic diamond, quite large and a natural green color with a slight blue overtone makes it virtually priceless. The Hope is also very unusual for the same reasons, but much more famous. The stone was originally a rather flat, blocky 110-carat rough. It was cut into a triangular pear of 68 carats, and then again into the 45.52-carat cushion cut it is today. The Conde Pink is a pear shaped 9.01-carat pink stone once owned by Louis XIII, also a naturally colored diamond. In January, 2002, I recieved an email from Terry J. Murray, in which he told me the following about a red diamond that had been auctioned off at Christies Auction House: "A rectangular-cut fancy red diamond of 0.73 carats sold for $536,000 per-carat." This was in a May 2nd, 2001 press release on the site. Thanks Terry! :)

In 1988, Sotheby's Auction House also sold a round, 0.90-carat, VS2 clarity, vivid green of natural color for $663,000 to an American collector. The per-carat price was over $736,000. This per-carat price is second to the 0.95-carat Hancock Red Diamond that sold also at Sotheby's for $880,000 (or $926,315 per-carat) on April 28, 1987. The stone is rumored to have been bought by a man representing the Sultan of Brunei, who is said to have one of the largest colored diamond collections in the world. All in all, a colored diamond is going to cost more than a colorless one, but colorless diamonds will probably always be more popular in the market.

Cut There are many many different types of diamond cuts. The most common is the round brilliant, which has 57 facets. There are several very common variations on the round brilliant - the oval, the marquise, some cushion cuts, and the pear. All of which, in standard form, have 57 facets. Other very common diamond cuts are the heart, the step, and the princess. The sky is the limit as far as diamond cuts go. The last I heard, there are 255 registered diamond cuts.

However, the ones I just mentioned are the most common because some exotic cuts can waste rough stone. Heart cuts have become very popular the past few years, partly because of the booming diamond industry, and the film "Titanic", which featured a large heart cut blue sapphire that was thrown into the ocean. The movie prop was fake. However, after the film's release, a jewelry company faceted a heart cut sapphire identical to the stone in the film, then mounted it in a necklace to match. People often confuse the Hope Diamond and the 'Heart of Ocean' - both were blue, and both were surrounded by smaller white stones. However, one is a heart cut and the other a cushion, and the 'Heart of the Ocean' is considerably larger than the Hope Diamond. I am perpetually irritated by people confusing the Hope with the 'Heart of the Ocean.'

Carat-Weight Carat weight is the most deciding factor as to the value of a diamond. A well cut diamond of SI1 clarity and a weight of 4.00 carats would be worth alot more than one of the same clarity, but weighing 1.60 carats and VS2 clarity.

The largest faceted diamond in the world is the Golden Jubilee, weighing 545.67 carats. It is a Fancy Brownish-Yellow color and "fire rose cushion cut." It is unusual also because it has a certain type of rare color banding. The second largest faceted diamond in the world is the Star of Africa, also known as the Cullinan I. It weighs 530.20 carats and is a pear shape with 74 facets. The third largest diamond in the world is the Incomparable. It is a golden yellow-orange color, pear shaped, and weighs 407 carats. The fourth largest faceted diamond in the world is the Cullinan II. It was cut from the same stone as the Star of Africa - aka Cullinan I. It weighs 317.40 carats and is a cushion cut.

Up until 2001, the most valuable diamond (price-per-carat) was the 0.95-carat fancy red Hancock Red that had been sold at auction at Christies, NYC, for $880,000 ($926,315 per-carat). The stone was apparently purchased by a buyer representing the Sultan of Brunei, who reputedly has one of the largest collections of fancy colored diamonds in the world. I am not exactly sure which diamond holds the world record for the highest price per-carat, but I am almost certain its no longer held by the Hancock Red. Time will tell!