Kimberlite: How to Identify a Raw Diamond
Diamonds are renowned for their beauty and high value. Still, before they become the polished gemstones seen in jewelry, they exist as raw diamonds deep underground. Raw diamonds are commonly found within kimberlite, an igneous rock type studied intensely by geologists and diamond miners for decades. This article will investigate kimberlite’s geology, formation process, and methods of identifying raw diamonds within it.
What is Kimberlite?
Kimberlite is a volcanic rock formed deep within the Earth’s mantle. It was named after Kimberley, South Africa, where this mineral’s first deposit was discovered in the late 19th century. Kimberlite typically contains olivine, pyroxene, other minerals, and diamonds.
Kimberlite is highly sought-after due to its abundance of diamonds. While diamonds can be found in other rock types, kimberlite is the world’s richest source of this gemstone. As a result, Kimberlite pipes – vertical conduits that bring magma from beneath the Earth’s crust up towards the surface – serve as major mining areas worldwide.
How is Kimberlite Formed?
Kimberlite formation is a complex process involving magma rising quickly through the Earth’s mantle, carrying fragments of rock and minerals from deep within. As this magma reaches the surface, it explodes, creating an impact crater known as a maar.
Kimberlite formation is unique due to its explosive nature. Unlike other volcanic rocks, kimberlite is formed from a volatile-rich magma under intense pressure that rises rapidly and cools rapidly – creating an expansive foam-like texture filled with gas bubbles – providing energy behind a kimberlite eruption.
Diamond Formation in Kimberlite
Diamonds are created deep within the Earth’s mantle. High pressure and temperature cause carbon atoms to bond, forming a diamond crystal lattice structure. Once exposed to kimberlite magma, these diamonds are brought up close and embedded in volcanic rock.
Scientists still need to comprehend how diamonds form in kimberlite fully. Diamonds are thought to form under extreme pressure and temperature conditions, possibly caused by plate collisions. Then, after being carried to the surface by magma from beneath kimberlite, these precious gems become embedded in volcanic rock.
How to identify Raw Diamonds in Kimberlite?
Diamond miners employ a range of methods to identify raw diamonds within kimberlite. This complex process necessitates using advanced technology and the expertise of geologists and mining engineers. Here are some of the methods employed in identifying raw diamonds within kimberlite:
Geophysical Surveys: Geophysical surveys are employed to locate kimberlite pipes that may contain diamonds. These investigations employ various techniques such as ground-penetrating radar, magnetometry, and electromagnetics to detect anomalies in the Earth’s subsurface that might indicate the presence of kimberlite.
Core Drilling: Diamond miners use core drilling to extract rock samples once a potential kimberlite pipe has been identified. These samples are then analyzed in a laboratory to detect diamonds and gauge their quality.
X-Ray Fluorescence (XRF): X-ray fluorescence is a nondestructive analytical technique used to identify the chemical composition of materials. Diamond mining checks for elements like nickel and chromium associated with diamonds in kimberlite rock.
Heavy Liquid Separation: Once the kimberlite rock has been extracted and analyzed, diamond miners use heavy liquid separation to separate the diamonds from it. That involves mixing the sample with something heavier like lithium metatungstate with a specific gravity higher than the rock and diamonds; this allows them to be easily extracted and further analyzed.
Microscopic Analysis: Once diamonds have been separated from their rock matrix, they are examined under a microscope to assess their size, shape, and quality. This data helps determine their value and whether they can be used in jewelry pieces.
Types of Kimberlite
There are various kimberlite types, each with its characteristics and properties. Here are the three primary varieties:
Group I Kimberlite: Group I kimberlite is the most common type in most diamond mines worldwide. A high magnesium and potassium content and an absence of aluminum identify it. Group I kimberlite often occurs alongside larger diamonds and has a distinctive blue-green hue.
Group II Kimberlite: Group II kimberlite is less common than Group I kimberlite and is primarily found in southern Africa. Its high magnesium content and low potassium and aluminum levels distinguish it. Group II kimberlite often occurs alongside smaller diamonds and has a brownish-red hue.
Group III Kimberlite: Group III kimberlite is the rarest kimberlite type and is only found in Canada and Siberia. It stands out due to its low magnesium and potassium contents and a high amount of aluminum. Group III kimberlite often appears alongside smaller diamonds and has an earthy greenish-brown hue.
In addition to these three main kimberlite types, there are also several subtypes with distinctive characteristics and properties. Some of the more common subtypes include:
Orangeite Kimberlite: This kimberlite type is distinguished by its high chromium content and vibrant orange color. It primarily occurs in South Africa and is often associated with smaller diamonds.
Ultrapotassic Kimberlite: This kimberlite type is distinguished by its high potassium and low aluminum content. It mainly occurs in Italy and is often associated with small diamonds and minerals like phlogopite.
Lamproite: Though not strictly speaking a kimberlite type, lamproite is another igneous rock often associated with diamonds. It has a high potassium content and low amounts of silicon and aluminum. Mainly found in Australia, lamproite often comes into contact with smaller diamonds.
How can you tell if the diamond you have purchased is from kimberlite?
There are several methods to determine if a diamond is from kimberlite. Here are some of the more popular methods:
Origin Certification: One way to tell if a diamond is from kimberlite is by checking its origin certification. Diamond mining companies usually issue certificates identifying the location of the gem; if the stone originates from a kimberlite pipe, this information will be included on the certificate.
Inclusions: Diamonds mined from kimberlite pipes often contain inclusions or small imperfections within the stone. These could include surrounding rock fragments and other minerals and elements present during formation. Under a microscope, these inclusions can be examined to determine their composition and confirm that the diamond originates from a kimberlite.
Geochemical Analysis: Geochemical analysis is a technique used to examine the chemical composition of diamonds. Diamonds found in kimberlite pipes often exhibit unique chemical signatures compared to those from other rocks. By analyzing a diamond’s chemical makeup, geologists can identify whether it likely originated from kimberlite.
Location: Finally, where a diamond was discovered can provide insight into whether it originated from a kimberlite pipe. Although diamonds can be found in many types of rock, kimberlite pipes are the most frequent source of diamonds. Therefore, if a diamond is discovered near an area where kimberlite pipes are known to occur, it’s more likely to come from one of these rocks than elsewhere.
Process of diamond extraction from kimberlite
Diamonds are extracted from kimberlite by using a variety of mining techniques. Here is an overview of the general steps involved in the diamond extraction process:
Exploration: Before establishing a diamond mine, geologists must first identify a kimberlite pipe containing diamonds. That involves conducting geophysical surveys, analyzing core samples, and mapping the area to ascertain its size and location within a kimberlite deposit.
Open-Pit Mining: Once a kimberlite deposit has been identified, diamond miners typically employ open-pit mining techniques to extract the rock from underneath. That involves scraping away topsoil and vegetation before using heavy machinery to dig an expansive pit. The excavated kimberlite rock is then taken away and transported to a processing plant for further processing.
Crushing and Screening: At the processing plant, kimberlite rock is crushed into smaller pieces and then screened to separate larger chunks from smaller particles. These latter particles are then sent through gravity and magnetic separation machines to extract diamonds from their rock counterparts.
X-Ray Sorting: Once the initial sorting process is completed, any remaining material is sent through an X-ray sorter. This machine uses X-rays to identify diamonds by their unique crystal structure that sets them apart from other minerals and materials. Afterward, a series of jets blow the diamonds into a collection container.
Final Sorting and Cleaning: After the diamonds have been extracted, they undergo a final sorting and cleaning process to separate them based on size, shape, and quality. Any remaining impurities or inclusions from the stones must be removed.
Selling Diamonds: Once the diamonds have been sorted and cleaned, they can be sold to diamond cutters, wholesalers, and jewelry manufacturers. The cost of these gemstones will depend on several factors, such as their size, quality, and origin.
Conclusion
Kimberlite is a scarce and unique volcanic rock that supplies diamonds to markets worldwide. Identifying raw diamonds within it requires various techniques such as geophysical surveys, core drilling, X-ray fluorescence imaging, heavy liquid separation processes, and microscopic examination.
Diamond mining is a highly specialized field requiring the expertise of geologists, mining engineers, and other specialists. Determining raw diamonds within kimberlite deposits is just one aspect of this industry. It also involves extracting, processing, and selling the stones themselves.
Diamond mining remains an integral industry worldwide, providing jobs and economic benefits to communities in many countries. As technology progresses and our understanding of kimberlite and diamond formation improves, we expect continued innovation and growth within this sector for many years.
