A raw diamond is the mineral in its natural, uncut, and unpolished state. Unlike the brilliant gems seen in jewelry, these stones are typically dull, crystalline, and may look like common gravel or greasy pebbles when first extracted. Finding these carbon crystals requires understanding geology, employing specific prospecting methods, and adhering to legal guidelines. This guide focuses on the practical steps and scientific details involved in small-scale, amateur diamond prospecting.
Understanding Diamond Geology and Deposits
Diamonds form under immense heat and pressure deep within the Earth’s mantle, approximately 90 to 125 miles below the surface. They are brought to the crust through explosive, deep-sourced volcanic eruptions, which solidify into cone-shaped formations known as primary deposits. These deposits are generally composed of kimberlite or the less common lamproite rock, which act as the source rock for all natural diamonds.
Over millions of years, weathering and erosion break down these volcanic pipes, releasing the contained diamonds. Water then carries these durable stones downstream, forming secondary or alluvial deposits in riverbeds, stream terraces, and coastal plains. For the average person, searching in these alluvial deposits is the most realistic and accessible way to find a raw diamond.
These secondary deposits are identified by the presence of specific, dense minerals that crystallized alongside diamonds in the mantle. Prospectors search for these indicator minerals, which include chromium-rich pyrope garnets, bright green chrome diopside, and magnesium-rich ilmenite. Finding a concentration of these heavy minerals suggests proximity to a diamond source, even if the primary pipe is far upstream.
Essential Tools and Prospecting Techniques
The process of searching for alluvial diamonds involves isolating heavy minerals from lighter sediment like sand and clay. This separation relies on the diamond’s high density (around 3.5 g/cm³), which is much greater than common stream material. Prospectors focus on sampling gravel beds where the water current naturally slows and concentrates heavier materials, such as behind large boulders or in bedrock depressions known as potholes.
Basic equipment includes a shovel for digging and a set of classifiers, which are screens with different mesh sizes. The material is first screened through a coarse mesh, such as a half-inch screen, to remove large rocks and debris. The remaining material is then washed and run through progressively finer screens, typically down to a 10-mesh or 20-mesh size, to discard fine silt and sand.
The concentrated gravel is then processed using a gold pan or a small sluice box. Panning involves swirling the material with water, allowing the densest particles, including diamonds and indicator minerals, to settle at the bottom while lighter material is washed away. A sluice box uses riffles—small barriers—to catch the heavy minerals as water flows over them, providing a more efficient way to process larger volumes of material.
Identifying a Raw Diamond
A raw diamond does not have the brilliant sparkle of a cut gemstone and can be easily overlooked, often resembling a piece of dull, translucent quartz. In their natural state, diamonds typically form distinct crystal structures. The most common are the octahedron, which looks like two pyramids joined at their bases, or a dodecahedron, a 12-sided shape. The surface of a rough diamond often has a characteristic greasy or waxy luster and may display growth features like trigons—small, triangular indentations.
The diamond’s extreme hardness is the most definitive field test, as it ranks a 10 on the Mohs scale. A genuine diamond crystal can scratch almost any other mineral, including corundum (ruby or sapphire), which ranks at a 9.
Another distinguishing feature is the diamond’s interaction with light and water. Raw diamonds tend to be translucent or cloudy, and their high refractive index means they will not look clear when viewed edge-on, unlike many quartz crystals. Diamonds also have a natural affinity for grease and an unusual property of repelling water, a characteristic once utilized in commercial grease tables to separate them from other minerals.
Legal Considerations for Diamond Hunting
Before beginning any search, establish the legal status of the land and the mineral rights. In most regions, productive diamond areas are already claimed by commercial entities, and recreational prospecting is strictly prohibited. Searching on private land without explicit, written permission from the landowner constitutes trespassing and can lead to severe penalties.
It is necessary to research local and state mining laws, as these regulations dictate whether an amateur can keep any mineral finds and what tools are permissible. Many jurisdictions require a prospecting permit or a “miner’s right” to legally search for and claim minerals. The most straightforward option for a beginner is to visit a dedicated public site, such as the Crater of Diamonds State Park in Arkansas, which operates under a unique “finders, keepers” policy.
Even at public access parks, there are often strict rules governing the type of equipment allowed, such as prohibitions on motorized tools or limits on the size of digging implements. Adhering to these laws prevents legal issues and ensures that any potential discovery is lawful.