In January of 1905 the world’s largest gem-quality clear diamond was found. The “Cullinan” diamond, found in Pretoria, South Africa, was a 3,106-carat diamond weighing 1.33 pounds.
According to History.com, the Cullinan was later cut into nine large stones and about 100 smaller ones, valued at millions of dollars. “The largest stone is called the “Star of Africa I,” or “Cullinan I,” and at 530 carats, it is the largest-cut fine-quality colorless diamond in the world. The second largest stone, the “Star of Africa II” or “Cullinan II,” is 317 carats. Both of these stones, as well as the “Cullinan III,” are on display in the Tower of London with Britain’s other crown jewels; the Cullinan I is mounted in the British Sovereign’s Royal Scepter, while the Cullinan II sits in the Imperial State Crown.”
The Royal Collection Trust notes that in its uncut state, the 10.1 x 6.35 x 5.9 cm diamond weighed 3,106 metric carats, and at this scale, coupled with its extraordinary blue-white color and exceptional clarity, made it the most celebrated diamond in the world.
Over 100 years and it still is the largest clear diamond found, but there have been plenty more of these giant sparkling colorless and colorful gems. The Cape Town Diamond Museum notes the 777 carat Millennium Star diamond as the second largest colorless diamond with the highest color rating of D in the world. The Congolese rough diamond at 890 carats was cut into a yellow-brown diamond that ended up weighing 407.48 carats. The Woyie River rough diamond weighed 770 carats and was dubbed one of the largest alluvial diamonds ever to be found. And the Sergio diamond (3167 carats), weighing slightly more than the Cullinan, is a carbonado diamond, a rare black diamond. And most recently we wrote about the Lulo Rose, a 170 carat pink diamond.
Diamonds are most often found in kimberlite pipes, carrot-shaped, volcanic rock formations. Diamonds started out as carbon that crystallized deep in the earth under great pressure and temperature. Volcanic activity brought the diamonds to the Earth’s surface in kimberlite magma. Erosion of kimberlite deposits over many years caused the released diamonds and indicator minerals. Advancing and receding glaciers dispersed and transported the eroded materials hundreds or thousands of miles away, creating alluvial deposits in which sometimes contain diamonds. However, most diamonds are found in the kimberlite itself.
Natural diamonds, both gem and industrial quality, are the product of either open pit or underground mining, in which diamonds are contained in those kimberlite pipes, or they are extracted from alluvial deposits in riverbeds, coastal, and undersea locations. Each scenario requires an efficient and streamlined mining process to recover the most diamonds in the most economical way.
While kimberlite is the most common source of diamonds, finding it doesn’t guarantee finding diamonds. In fact, few kimberlite pipes actually prove worthwhile to pursue. Miners determine if a kimberlite pipe is worth pursuing by conducting regional sampling schemes and airborne geophysical surveys in a precise search area. Once a list of the best targets is assembled, grade analysis is done to find out if the kimberlite is sufficiently diamondiferous. Kimberlites are known to contain high concentrations of magnetite (strongly magnetic iron ore) and ilmenite (a black iron titanium oxide mineral)
Portable XRF instruments provide fast acquisition of geochemical data for ore deposit modeling, easily determining elemental constituents for most natural low concentration samples, as well as high grade ore concentrates. XRF (X-ray fluorescence) is a non-destructive analytical technique used to determine the elemental composition of materials.
XRF analyzers determine the elemental composition of a sample by measuring the fluorescence (or secondary) X-ray emitted from elements in a sample when those are excited by a primary X-ray source. Each of the elements present in a sample produces a set of characteristic X-ray lines (“a fingerprint”) that is unique for that specific element, which is why XRF spectroscopy is an excellent technology for qualitative analysis and quantitative determination of material composition. (For more information about XRF, download this ebook: Portable XRF Technology for the Non-Scientist.)
Ore-grade assessment utilizing XRF technology helps manage blasting, excavation, and hauling activities, optimizing the site blend provided to the concentrator while preventing grade dilution or the erroneous transport of ore to the waste dump. One can rapidly delineate ore boundaries and quickly identify increasingly low-grade deposits as well as instantly flag grade, sub-grade, and waste.
It seems that when it comes to diamonds, XRF technology may be a miner’s best friend.
- Explore more aspects of mining in our Mining & Minerals virtual storefront
Editor’s Note: Portions of this article were excerpted from previously published articles.