THE FOUR LARGEST SOUTH AFRICAN DIAMONDS
Name 1. Golden Jubilee 2. The Great Star of Africa (Cullinan l ) 3. The Lesser Star of Africa (Cullinan ll ) 4. Centenary Polished Weight (in carats) 545.67 530.20 (3106 rough carats) 317.40 273.85 Last known owner/location King of Thailand The British Royal Sceptre British Imperial State Crown De Beers * The Star of Sierra Leoneí is the largest diamond recovered from an alluvial source in Africa.
THE FOUR C'S OF DIAMOND QUALITY
When looking to purchase a diamond it is important to remember the ìFour Csî, the characteristics which give the diamond its quality and value. These are: Cut, Colour, Clarity and Carat-weight.
Cut: A diamondís cut is what gives it sparkle and fire. The better the proportions, the better the diamond is able to handle light, creating more sparkle and scintillation.
Colour: The majority of diamonds range from those with barely perceptible yellow and brownish tints up to the very rare pinks, blue and greens which are known as ëfanciesí. The best colour for a diamond is however colourless.
Clarity: Most diamonds contain tiny inclusions, not discernible to the naked eye. The fewer and smaller they are, the less likely they are to interfere with the passage of light through the diamond, and therefore the more rare and beautiful it will be.
Carat-weight: One carat is divided into 100 ëpointsí, so that a diamond of 75 points weighs 0,75 carats. (1 carat = 0,2 grams). Two diamonds of equal weight can therefore have very different values, depending on their cut, clarity and colour.
DIAMOND TRIVIA
The Seven major diamond mining countries of the world: Botswana, Russia, South Africa, Angola, Namibia, Australia, Democratic Republic of Congo.
Diamonds are also mined in these countries: Brazil, Guyana, Venezuela, Guinea, Sierra Leone, Liberia, Ivory Coast, Ghana, Central African Republic, Tanzania, China, Indonesia, Zimbabwe, India.
DIAMONDS : THE BACKGROUND MINERALOGY, GEOLOGY AND GEOMORPHOLOGY OF DIAMOND FORMATION.
A short overview of crystal formation and the geology and geomorphology of the southern part of the African Continent is presented to assist the reader in an understanding in the placement of diamonds, both in primary volcanic intrusions and secondary alluvial deposits.
The crystallization of diamonds and the formation of primary deposits, i.e. diamondiferous kimberlite pipes and dykes (or "fissures" as they are called), requires a special set of conditions in and below the earth's crust with special geologic events.
Diamond crystallization : Diamond crystallization takes place at pressures in excess of 50 kilobars and temperatures in excess of 2000 degrees celsius. This leads to the strongest and most compact tetrahedrally coordinated structure found in all of nature, ie. diamond. Crystallization takes place within the garnet peridotite mantle of the earth at least 120 kilometers beneath the surface of the crust.
Stable continental crust : A long period of stability is required in sections of the earth's crust known as continental platforms below which diamonds can crystallize in association with eclogite (high pressure garnet pyroxene rock) within the subcrustal mantle peridotite.
Uplift and fracturing : Uplift of the earth's crust which leads to the partial melting of the parts of the mantle, and also to the development of large tensile cracks or fracture zones extending through the crust and penetrating into the mantle. These allow the melted fluids and associated gases, which are under great pressure, to escape upwards dragging fragmented masses of solid rock and loose mineral grains with them, eventually reaching the surface explosively and filling the fractures with the ultrabasic hypabyssal agglomeratic material called kimberlite.
ABOUT DIAMONDS
THE WORD "DIAMONDí"ORIGINATES FROM THE GREEK WORD "ADAMAS", MEANING UNCONQUERABLE OR INVINCIBLE.
Ancient Greeks believed that diamonds were splinters of stars that had fallen on earth. Some said that they were the tears of gods. Legend has it that there existed an inaccessible valley somewhere in Central Asia, a carpet of diamonds covered it. It was patrolled by prehistoric birds of prey and guarded by venomous snakes. However, the truth is that the exact origin of diamonds is still a mystery, to scientists and geologists.
The diamond is the hardest of all gemstones known to man, yet it is the simplest in composition. It is common carbon, like the graphite in lead, but has a melting point of about 4 000 degrees centigrade, which is approximately two and a half times greater than the melting point of steel.
HOW ARE DIAMONDS FORMED?
Diamonds were formed as long ago as 3,5 billion years, under conditions of great heat and pressure, deep inside the earth. This correlates with the earliest stages of the development of our planet, estimated to be in the region of 4,5 billion years old.
Volcanic eruptions carried the diamonds to the surface of the earth millions of years ago. Diamonds are found in cone-shaped pipes of rock called kimberlite. These pipes have been weathered and their diamonds dispersed by rivers to far-lying areas, such as coastlines.
There are two types of diamond sources for mining: The primary and secondary deposits are kimberlite and alluvial reserves. Exploration of kimberlite and alluvial diamonds require different mining methods. ìAlluvialî mining is the recovery of diamonds from current and historic river beds, sea or seashores, also referred to as "wet" mining. "Pipe" mining involves the extraction of diamonds from volcanic pipes, also referred to as "dry" mining or traditional open-cast mining.
ALLUVIAL DIAMONDS IN SOUTH AFRICA
"Feeling somewhat tired, I sat down in the shade of a tree, when I suddenly noticed, in the glare of the strong sun, a glittering pebble some yards away. I became curious and picked up this beautiful stone. I was, at the time, wearing a corduroy suit, and simply put the pebble in my pocket. I did not feel at all excited at finding such a beautiful stone."
As news of this discovery spread, people from all walks of life flocked to the area in their thousands. The search for diamonds had spread from the Orange River to the Vaal River and by 1869 the ìRiver Diggingsî were a hive of activity. 1871 saw a most significant discovery of dry deposits when Fleetwood Rawstorneís ìRed Cap Partyî discovered diamonds on a hillock called Colesberg Kopje. Diggers soon demolished the hillock and the result was the Kimberley Mine, or as it is better known today, the Big Hole.
Pressure maintenance : As the kimberlite materials flow upwards along crustal fractures they enter lower pressure regimes which would cause diamonds held within the stream to become unstable. At these lower pressures the carbon would revert to the graphite structure. The presence of hard andesite lava formations would therefore have a direct bearing on the physical conditions within the stream of upward moving intrusive kimberlite. When is kimberlite reaches about 1 kilometer from the earth's surface, explosive eruption occurs. This causes a rapid decrease intemperaturesthe and diamond retension ("freezing") of carbon in the diamond structure.
Erosion of the upper crust materials : The uplifted surface of sedimentary and volcanic materials together with the diamondiferous kimberlite in the highest levels of the kimberlite pipe is exposed to climate, undergo weathering and erosion. The loose material mineral grains are transported by streams and river systems which drain off the uplifted central plateau and end up in the newly formed basins. As the rivers deepen their channels they encounter rock formations and structures which differ in hardness and resistance to scouring. This produces resistant rock formations where hollows / gullies / depressions develop and act as trapsites on the upstream and down stream sides of the river. Diemonds and well rounded materials are trapped in these trapsites or drop - off zones. These can be located along the current courses of rivers, the riverbeds and terraces, even as far as marine terraces along the coastline and near river outlets. The deeper and larger the potholes or trapsites, the greater the probability of finding larger numbers and sizes of diamonds.
Climate : Climate plays a significant role in either exposing or obscuring the presence of kimberlite pipes in any region. In semi - arid climate, prominent calcrete cappings would form at the surface of kimberlite pipes in areas where the country rock consists of shale and dolomite, and bushfilled pans would form in areas where quartzite, dolorite or branded ironstone make up the country rock. In tropical basin regions with very high rainfall, the pipies would be obscured by thick layers of weathered material and sediments.
DIAMOND MINING METHODS
Exploration of kimberlite and alluvial diamonds require different mining methods. ìAlluvialî mining is the recovery of diamonds from current and historic river beds, sea or seashores, also referred to as "wet" mining. "Pipe" mining involves the extraction of diamonds from volcanic pipes, also referred to as "dry" mining or traditional open-cast mining. Site specific characteristicts will dictate the method or combination of methods to extract the reserves.
"Dry" mining makes use of an open cast excavation by means of earthmoving equipment. "Wet" mining makes use of solids dredging technology and the availability of water as a means of transport to extract the diamondiferous gravels for processing. The processing of extracted gravels can be performed by a hand or mechanical jig, vibrating or spinning tables and various other advanced methods. Land mining equipment has advanced to the point where it is difficult to improve on the efficiency of current processing methods and equipment. Dredging of diamonds can be done by the simplest of means at artisinal level, or a solids dredge pump, or dredging barge or at an advanced level, by a dredging remote controlled submersible crawler.
DIAMOND CLASSIFICATION
A diamond weight is the simplest of its characteristics to measure and it is used to calculate one aspect of the value of the diamond. One carat is a unity of weight and it is equal to a fifth of a gram. Each carat is divided into 100 points, for example, a quarter carat is 25 points and half a carat is 50 points and so on.
arger diamonds are more valuable than smaller ones from the simple fact that they are found in nature less frequently than smaller ones. The larger the diamond is, the more rare it is, and therefore, the price per carat increases as the diamond gets larger. However, carat weight has no bearing on diamond color, clarity, or cut.
