How Do Diamonds Form?
Natural diamonds form deep within the Earth's mantle under extreme conditions of high pressure and temperature. The formation process takes place over billions of years. Here's a step-by-step breakdown of how natural diamonds form:
Source Material: The primary ingredient for diamonds is carbon. Given that Earth's early atmosphere and volcanic emissions are rich in carbon compounds,
there's plenty of raw material.
Depth and Pressure: Diamonds typically form at depths between 187 to 118 miles below the Earth's surface. Here, pressures are around 725,000 pounds per square inch or more.
High Temperatures: The temperatures required for diamond formation range from about 1,832 to 2,372 degrees Fahrenheit.
Crystal Growth: Under these extreme conditions, carbon atoms bond in a unique dense isometric-hexoctahedral crystal lattice structure.
Transport to the Surface: Diamonds reach closer to the Earth's surface through volcanic eruptions. These eruptions create kimberlite and lamproite pipes, which are the primary sources of diamond mining. The molten rock (magma) from deep within the Earth rises rapidly, carrying with it pieces of the mantle, including diamonds.
Preservation: Once the magma reaches the surface, it cools and solidifies to form kimberlite or lamproite rock. Diamonds are found within these rocks. If the journey to the surface is too rapid or if the diamonds are exposed to low pressures, they might transform into graphite.
Discovery and Mining: Most diamond deposits are found in Africa, Russia, Canada, and Australia. Miners extract diamonds either from primary deposits (in kimberlite or lamproite pipes) or from secondary deposits where diamonds have been transported by water to riverbeds or the ocean shore.
The age of most diamonds is estimated to be between 1 billion to 3.5 billion years old, making them witnesses to a considerable portion of Earth's long history.
The carbon required for natural diamond formation originates from both organic and inorganic sources deep within the Earth. These sources have contributed carbon to the mantle over geological time scales. Here are some primary sources of carbon for natural diamonds:
Primitive Carbon: This is carbon that has been in the mantle since the Earth's formation. It is believed to be a primary source of carbon for diamonds and is considered inorganic.
Subducted Oceanic Crust: As tectonic plates move, oceanic plates can dive or "subduct" beneath continental plates. Oceanic crust contains both basalt (a type of igneous rock) and sediments from the ocean floor. These sediments can contain organic carbon from decaying marine organisms. As the crust is pulled into the mantle, the heat and pressure can release this carbon, making it available for diamond formation.
Subducted Carbonates: Carbonate rocks, like limestone and dolomite, can be carried into the mantle through the process of subduction. When these carbonate rocks are subjected to the extreme conditions in the mantle, they can release carbon dioxide. This CO₂ can then be reduced to elemental carbon, which can contribute to diamond formation.
Carbon from Deep Earth Reservoirs: The Earth's mantle, especially the deeper parts, might have isolated reservoirs of ancient carbon. Some diamonds, known as "deep-source diamonds," might form from this carbon.
Organic Material: In certain diamond-bearing rocks (like eclogites), there's evidence that the carbon comes from organic material, possibly from ancient algae or microorganisms that existed billions of years ago. The isotopic signatures of carbon in these diamonds can sometimes give clues about their organic origins.
It's worth noting that the exact source of carbon for any given diamond is complex and can vary depending on the location and geological history of the diamond deposit. Advanced analytical techniques, such as studying the isotopic ratios of carbon and nitrogen in diamonds, can provide insights into the likely sources of carbon for particular diamonds.
Natural diamonds have a distinct crystal structure & atomic structure that imparts them their renowned hardness, brilliance, and other unique properties. Here's a detailed overview of the rough natural diamond crystal structure:
Crystal System: Diamonds crystallize in the cubic (or isometric) crystal system. This means that the basic crystal shape has three equal axes oriented at 90 degrees to each other.
Lattice Structure: The atomic arrangement in a diamond is a repeating or periodic array, which is often referred to as a crystal lattice. In the case of diamond, it's a face-centered cubic (fcc) lattice. Each carbon atom in a diamond is tetrahedrally bonded to four other carbon atoms. This arrangement and the strength of the carbon-carbon bond give diamonds their extraordinary hardness.
Octahedral Form: The most common form for rough diamonds is the octahedron, which looks like two pyramids base to base. Many diamonds are found with this shape, but they can also be found in other forms such as cubes or dodecahedra, or a combination of these forms.
Inclusions and Imperfections: Natural diamonds often contain inclusions or imperfections. These can be other minerals, fractures, or even tiny pockets of fluid. These inclusions can affect the clarity of the diamond. The type and distribution of inclusions can also provide insights into the diamond's formation and geological history.
Growth Features: As diamonds form and grow, they can exhibit a variety of external and internal growth features. These might include growth zones, which are layers of the diamond that have grown at different times or under slightly different conditions. Sometimes, diamonds can exhibit a 'trigonal' or 'macle' shape, indicating twinning in the crystal structure.
Color and Nitrogen
: Pure diamonds are transparent and colorless. However, most diamonds contain minute quantities of other elements as impurities. Nitrogen is the most common impurity in diamonds and can impart a yellow color to the stone. The arrangement of nitrogen atoms in the crystal lattice (whether isolated, in pairs, or in larger aggregates) can influence the diamond's color and its behavior under UV light.
Surface Features: Rough diamonds can often exhibit surface features, such as trigons (triangular etchings), which can provide insights into the diamond's growth and the conditions in the mantle where it formed.
The properties and characteristics arising from a diamond's crystal structure make it not only a sought-after gemstone for jewelry but also an invaluable material for industrial applications where hardness and thermal conductivity are vital.
The term "crystal habit" refers to the common or characteristic shape (or assembly of shapes) that individual crystals or aggregates of crystals tend to form. In the case of natural rough diamonds, several crystal habits are typically observed. Here's a breakdown:
Octahedral: This is the most common crystal habit for diamond. It resembles two pyramids placed base-to-base and has eight faces, each of which is an equilateral triangle. Most natural diamonds are found in this shape or show evidence of this form, even if they are somewhat distorted or have additional faces.
Cuboctahedral: A combination of the octahedron and cube, these diamonds have faces of both the octahedron and the cube present.
Cubic: Though less common than octahedral diamonds, some diamonds do form as cubes with six square faces.
Dodecahedral: These diamonds have twelve faces, but unlike the octahedral diamond, the faces are not triangular but are four-sided with an overall rhombic shape.
Macle: This is a flattened, triangular diamond crystal, often twin crystals. Macles are typically formed by contact twinning, where two diamond crystals share some of the same lattice points in a symmetrical manner. Macles are often used for fancy cuts, like the heart or marquise shapes, due to their flat, triangular shape.
: This form includes 24 faces and is a more complex habit than the basic forms listed above.
It's worth noting that while these habits are the idealized shapes, real-world diamonds often display irregularities. They might be distorted, have rounded edges, or show growth features that deviate from these perfect shapes. These irregularities can be caused by various factors, including the conditions of formation, the presence of other minerals, and disturbances during the diamond's ascent to the Earth's surface.
Furthermore, the surface of a rough diamond can also have specific features like trigons (small, triangular growth markings) that can provide additional insight into its growth history and conditions of formation.
Diamond and Graphite
Diamond and graphite are both allotropes of carbon, which means they are made entirely of carbon atoms but have different atomic structures. These structural differences lead to vastly different physical properties. Let's delve into a comparison of these two forms of carbon:
: Each carbon atom in diamond is tetrahedrally bonded to four other carbon atoms. This forms a three-dimensional network, resulting in a crystal lattice that gives diamonds their characteristic hardness.
Graphite: In graphite, each carbon atom is bonded to three other carbon atoms, forming hexagonal layers. These layers can slide past each other easily because they are held together by weak van der Waals forces
: It is the hardest known natural material. This hardness arises from the strong dense covalent bonds between carbon atoms in a three-dimensional matrix.Graphite
: It is soft and slippery, which is why it's used as a lubricant and in pencils. The layers can slide past one another with ease.
: Generally, a diamond is an insulator; it does not conduct electricity well.Graphite
: It's a good conductor of electricity due to the presence of free electrons in its structure, which can move between the layers.
: Transparent and refractive, diamonds can split light into its constituent colors, leading to the "fire" seen in gem-quality diamonds.
Graphite: It's opaque and black in color.
: Has a high density due to the compactness of its tetrahedral structure.Graphite
: Has a lower density than diamond because of the space between its layered structures.
: Exceptionally good thermal conductor, better than most metals. This property is again due to its strong covalent bonding and crystal structure.
Graphite: Also a good conductor of heat, but not as effective as diamond.
: Used for jewelry, industrial cutting and drilling tools, and scientific applications due to its hardness, brilliance, and ability to refract light. Synthetic diamonds are also used in electronics and other industries.
Graphite: Used in pencils (the "lead" in pencils is graphite), as a lubricant, in batteries, and in various industrial applications.
Despite graphite and diamond being, composed of the same element, the contrasting structures of Graphite and diamond result in their divergent properties. A major difference between diamond and graphite is the difference in very strong covalent bonds. This dichotomy is a powerful demonstration of how atomic arrangement can drastically change the properties of a substance.
How Hard Is Diamond?
Diamond is renowned for its exceptional hardness. On the Mohs hardness scale of mineral hardness, which ranges from 1 (talc) to 10 (diamond), diamond is rated as 10, making it the hardest natural material known.
The Mohs scale is a relative scale, meaning it ranks minerals based on their ability to scratch other minerals. A material with a higher Mohs value can scratch any material with a lower value. Therefore, a diamond can scratch any other mineral, but no other natural mineral can scratch a diamond.
They are formed from carbon subjected to intense heat and pressure deep within the Earth's mantle, at depths ranging from 87 to 120 miles. This process, which can span 1 to 3.3 billion years, alters the diamond's molecular structure, causing the molecules to bond closely together in what's called covalent bonding. This tight molecular bond is what gives diamonds their unparalleled hardness.
The hardness of diamond is attributed to the strong covalent bonding between its carbon atoms in a three-dimensional tetrahedral structure. Each carbon atom in diamond is bonded to four other carbon atoms. This arrangement, combined with the strength of the carbon-carbon bond, results in its extraordinary hardness.
However, it's important to note that while diamonds are incredibly hard, they are not indestructible. Diamonds can be cleaved or fractured if struck with a sharp blow in certain directions, as they have planes of atomic weakness. This property is exploited when diamonds are cut and shaped for jewelry and industrial uses.
Gem vs. Industrial Diamonds
Gem-quality diamonds and industrial diamonds differ primarily in terms of their aesthetic and physical properties. While both are composed of carbon and share the innate hardness of diamonds, their applications differ based on their quality, clarity, and overall appearance. Here's a breakdown of the differences between the two:
Quality and Clarity:
: These diamonds possess the clarity, color, and quality suitable for jewelry. They typically have fewer inclusions and blemishes, and their internal and external characteristics make them desirable for use in engagement rings, necklaces, earrings, and other jewelry pieces.
Industrial Diamonds: These diamonds often have numerous inclusions, blemishes, or subpar color, which makes them unsuitable for jewelry. Their appearance is generally less appealing than gem-quality diamonds.
: Primarily used in jewelry making. They are cut, polished, and crafted into various pieces of jewelry to showcase their brilliance and fire.
Industrial Diamonds: Used in various industrial applications due to their hardness. They are used in cutting, grinding, drilling, and engraving tools. They can be found in oil drilling bits, saw blades, and grinding wheels.
: Generally, they are more expensive due to their rarity and the high demand in the jewelry market. Factors like carat (size), clarity, color, and cut determine their price.Industrial Diamonds
: They are less expensive than gem-quality diamonds. While they are valuable for industrial uses, their aesthetic imperfections decrease their market value in the jewelry sector.
: While many come from natural sources, advancements in technology have made it possible to produce gem-quality diamonds synthetically. These lab-created diamonds share the same physical and chemical properties as natural diamonds.Industrial Diamonds
: Many of the diamonds used in industrial applications are synthetic. It's more cost-effective to produce the vast quantities of diamonds needed for industrial purposes in labs than to mine them.
Shape and Cutting:
: These are meticulously cut and shaped to maximize their brilliance and fire. Common shapes include round, princess, oval, and marquise, among others.Industrial Diamonds
: The emphasis is on their functional properties rather than their appearance, so they are not finely cut or polished like gem-quality diamonds.
Diamond Gemstone Quality Factors
When assessing the quality and value of a diamond gemstone, professionals typically refer to the "Four Cs" - Carat, Cut, Color, and Clarity. Each of these factors plays a crucial role in determining the overall quality and price of a diamond. Here's a deeper look into each of these factors:
The weight of a diamond is measured in carats. One carat is equivalent to 200 milligrams.
The price per carat generally increases with carat size because larger diamonds are rarer and, therefore, more valuable.
This refers to how well the diamond has been cut, shaped, and faceted. It does not refer to the shape of the diamond (e.g., round, oval, princess, etc.).
The cut affects a diamond's brilliance and sparkle. Factors such as depth, table size, symmetry, and polish are considered when grading the diamond's cut.
The quality of the cut is usually graded on a scale from Excellent to fair. A well-cut diamond will reflect light within itself, from one mirror-like facet to another, dispersing light and reflecting it through the top of the stone, leading to the gem's brilliance.
Diamonds are graded on a color scale established by the Gemological Institute of America (GIA) that ranges from D (colorless) to Z (light yellow or brown in tone).
Generally, the more colorless a diamond is, the higher its quality. However, diamonds can come in a variety of colors, including blue, green, and pink. These are known as "fancy" diamonds and are graded on a different scale.
Clarity refers to the presence of internal or external imperfections, called inclusions and blemishes, respectively.
The GIA's clarity scale includes six categories: Flawless (no inclusions or blemishes visible under 10x magnification), Internally Flawless (no inclusions visible under 10x magnification), Very Very Slightly Included, Very Slightly Included, Slightly Included, and Included.
Diamonds with fewer or no inclusions are more valuable because they are rarer and clearer, allowing more light to pass through them.
Apart from the Four Cs, there are other factors that can also influence the value and appearance of a diamond:
Fluorescence: Some diamonds can emit a visible light when exposed to ultraviolet (UV) rays, which is referred to as fluorescence. Depending on its strength and color, fluorescence can either increase or decrease a diamond's value.
Shape: While not a direct quality factor like the Four Cs, the shape of a diamond (e.g., round, oval, marquise, pear, etc.) can influence individual preference and demand, affecting its market price.
Treatments: Diamonds can undergo various treatments to enhance their appearance, such as laser drilling to remove inclusions or high-temperature annealing to improve color. Treated diamonds generally fetch a lower price than untreated stones.
Synthetic diamonds, also known as lab-grown or man-made diamonds, and natural diamonds both have the same physical, chemical, and optical properties, as they are both composed of carbon. However, there are significant differences in their origins, production methods, value, and certain characteristics. Let's break down these differences:
: Formed deep within the Earth's mantle over a billion years ago under conditions of extreme heat and pressure. They are brought closer to the surface through volcanic eruptions via kimberlite pipes.
Synthetic Diamonds: Grown in labs over weeks or months using advanced technological processes that replicate the conditions under which diamonds naturally develop.
: Mined from the Earth, which involves extraction processes that can be labor-intensive & costly.
Synthetic Diamonds: Produced using one of two primary methods.
High Pressure High Temperature (HPHT): emulates the natural conditions of diamond formation by applying extreme heat and pressure to a carbon source.
Chemical Vapor Deposition (CVD): Involves breaking down a carbon-containing gas (like methane) in a vacuum chamber, which then deposits onto a substrate, allowing diamond to grow layer by layer.
: Typically more expensive due to the costs associated with mining, the rarity of certain diamonds, and their long geological formation process.Synthetic Diamonds
: Significantly less expensive to produce, often resulting in a lower market price compared to natural diamonds of similar quality. However, prices can vary based on production costs and quality.
Environmental and Ethical Impact:
: Mining can have significant environmental impacts, including habitat destruction and carbon emissions. Additionally, some diamond mines have been associated with funding conflicts, leading to the term "blood diamonds." However, initiatives like the Kimberley Process aim to ensure diamonds are conflict-free.
Synthetic Diamonds: While lab-grown or man-made diamonds are often marketed as an environmentally friendly alternative to mined diamonds due to the avoidance of ecologically harmful mining practices, they do come with their own set of environmental concerns. Here are some of the potential negative environmental impacts associated with producing synthetic diamonds.
The two primary methods for producing synthetic diamonds, High-Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD), both require a significant amount of energy.
For some diamond-producing labs, if the energy source is non-renewable (like coal or natural gas), this results in substantial carbon emissions. The environmental footprint can be significant if the lab isn't powered by renewable energy sources.
Diamond production, especially using the HPHT method, can require vast amounts of water for cooling. If the water isn't managed or recycled properly, this can strain local water resources.
Producing synthetic diamonds might involve the use of certain chemicals that, if not handled or disposed of correctly, could pose environmental risks.
For the CVD process, a carbon source is needed. Methane, a potent greenhouse gas, is often used. While most of the methane is broken down in the process, there is potential for emissions.
The machines used for synthetic diamond production generate a significant amount of heat. If not managed correctly, this could contribute to localized heating in facilities and demand more energy for cooling.
Equipment and Resource Use:
The machines and equipment used in synthetic diamond production are made from materials extracted from the earth, and their manufacture, use, and disposal all come with environmental costs.
Inclusions and Imperfections:
Natural Diamonds: Often contain unique inclusions or imperfections, which can be seen as nature's fingerprints. These can sometimes be used to trace the diamond's origin.
Synthetic Diamonds: While they can also have inclusions, the types and patterns of these inclusions can differ from those in natural diamonds. Some synthetic diamonds, especially high-quality ones, might have fewer inclusions than their natural counterparts.
Both types of diamonds can be distinguished using specialized equipment. While it might be challenging to differentiate them with the naked eye, trained gemologists with appropriate tools can detect differences in growth patterns, inclusions, and other characteristics.
: Traditionally valued for their rarity and the idea that they represent billions of years of Earth's history.
: As technology advances and public awareness grows, synthetic diamonds are becoming more accepted and mainstream in the jewelry market. However, they are becoming cheaper and cheaper to produce, values are dropping and they are not transportable value.
Gem-grade diamonds, often referred to as gem-quality diamonds, are the diamonds deemed suitable for use in jewelry due to their clarity, color, cut, and carat weight. While diamonds themselves are relatively common, gem-quality diamonds are more rare when considered within the entirety of diamond deposits. Here are some points to consider:
Of all the diamonds mined globally, only about 20% to 30% are considered gem-quality. The rest, often referred to as industrial diamonds, are used for various industrial applications due to their hardness and other physical properties but lack the clarity and color required for jewelry.
Rarity Among Gem-Quality Diamonds:
Within the subset of gem-quality diamonds, there is a range of quality. Diamonds with the highest color grades (near colorless to colorless) and clarity grades (with few to no inclusions or blemishes) are rarer.
Larger gem-quality diamonds are also rarer. For instance, finding a 2-carat diamond is not merely twice as hard as finding a 1-carat diamond; it's exponentially rarer.
Fancy Color Diamonds:
While most gem-quality diamonds are graded on their lack of color, diamonds can come in a variety of hues, including blue, green, pink, red, and yellow. These are known as "fancy" diamonds.
Among these, some colors are particularly rare. For example, red and blue diamonds, like the famous Hope Diamond or the Red Diamond, are incredibly rare and can fetch higher prices per carat than even the highest quality colorless diamonds.
Origin and Sources:
Certain high-quality diamonds are rarer depending on their geographic origin. For instance, pink diamonds from the Argyle mine in Australia are highly sought after due to their unique hue and limited availability.
Natural vs. Synthetic:
With the advancement of technology, lab-grown or synthetic diamonds have entered the market. These diamonds are physically, chemically, and optically identical to natural diamonds but can be produced in a matter of weeks. The availability of lab-grown diamonds has introduced a new dimension to the conversation about rarity, as they can be produced more consistently and in desired qualities.
However, natural gem-quality diamonds, formed over millions to billions of years, still hold a unique allure for many due to their ancient origins and the perception of rarity.
Industrial-grade diamonds, which make up the majority of diamonds mined, are not suitable for use in jewelry due to their inclusions, blemishes, or subpar color. However, they have a wide range of applications in various industries because of the exceptional hardness and other properties of diamonds. Here are some of the primary uses of industrial-grade diamonds:
Cutting tools and Grinding Tools:
Diamonds are embedded in drill bits or saw blades to cut through hard materials like stone, concrete, and metals. Diamond-tipped tools provide superior cutting efficiency and longevity compared to other materials.
Diamond powders and grits are used as abrasives to grind, shape, and polish other hard materials. They are commonly used in lapidary work and in the production of other gemstones.
Diamond-tipped drill bits are essential in the oil and gas industry for drilling through the Earth's crust. Their durability and resistance to heat make them ideal for such demanding tasks.
Diamonds are excellent conductors of heat. In some high-tech applications, diamond slivers or layers are used to dissipate heat, acting as heat sinks.
In machining and metalworking, diamond "dressers" are used to shape, sharpen, and maintain the grinding wheels themselves.
The incredible hardness of diamond makes it useful in high-pressure devices used in experimental physics and materials science.
Some high-performance speakers use diamond domes in tweeters to achieve a broader frequency range and better overall sound quality.
Diamonds are used in certain surgical tools, like scalpels, due to their sharpness and precision.
Because of the diamond's unique electronic properties, there's ongoing research into its use in semiconductors and other advanced electronic applications.
Not the kind in your house, but specialized windows for devices and chambers that require durable, transparent coverings that can withstand harsh conditions.
In conclusion, natural diamonds form deep within the Earth's mantle under extreme conditions of high pressure and temperature over billions of years. The process involves carbon-rich materials, extreme depths and pressures, and high temperatures, leading to the dense unique isometric-hexoctahedral crystal lattice structure responsible for their exceptional hardness. Diamonds are transported to the surface through volcanic eruptions, primarily via kimberlite and lamproite pipes, and are found within cooled magma in these rock formations. Most diamonds are discovered and mined in Africa, Russia, Canada, and Australia. Gem-grade diamonds, suitable for jewelry, are rare, with the "Four Cs" - Carat, Cut, Color, and Clarity - being crucial factors in determining their value. Synthetic diamonds, produced in laboratories, share the same properties as natural diamonds but are generally less expensive and do not hold their value. Industrial-grade diamonds, more common than gem-quality ones, are used for cutting, grinding, drilling, and polishing in various industrial applications due to their hardness and durability.