Rough Diamond Buying Guide: How to Choose a Raw Diamond Shape - Octahe – The Raw Stone

If you've ever tried to buy a rough diamond, then you already know that the color, clarity, size and shape define a rough diamond, help you appraise its value and understand whether or not it's a stone that will work for you and your needs. If you're not familiar just yet, we are here to help you get acquainted with how to shop for rough diamonds. Each of the aforementioned factors - color, clarity, size and shape - are important, and each has its own complexity. In this blog post, though, we are going to focus on shape. Specifically, the octahedron.

A rough diamond octahedron sourced from Canada

An octahedron is shaped like two pyramids placed together, base to base. It is one of the most common shapes of rough diamonds, and is particularly sought after for both rough diamond jewelry, and for cutting purposes. Here's what a raw diamond octahedron looks like geometrically:

Octahedron geometric image

The octahedron is particularly prized for rough diamond jewelry because of its proportionate, geometric shape that sets extremely well in various types of rings, earrings, necklaces, etc. It can easily be adorned by other stones or masterful metalwork in the setting, but it can also stand alone in a jewelry piece such as an engagement ring and appear classic and majestic. Octahedrons tend to be very angular, show their inner structure very clearly and refract the light intensely and beautifully. Here's one of our favorite examples of an unadorned rough diamond octahedron engagement ring by renowned contemporary jeweler Kara Daniel Jewelry.

Tension set rough diamond engagement ring with octahedron by Kara Daniel Jewelry

The patterning on the surface of the above rough diamond octahedron is called "trigons". These are small triangular crystalline structures that can appear on the surface of rough diamonds. This particular octahedron has many trigons, but similarly, octahedrons can also have perfectly smooth, clear surfaces.

Rough diamond octahedrons are also prized for their ability to be cut and polished fairly straightforwardly into round brilliant diamonds and princess cut diamonds. The octahedron is first cleaved or sawn at its center into two pyramid-shaped diamonds. On our site, we call these sawn diamonds. Here's an example of one on our inventory:

Sawn raw diamond octahedron

This sawn octahedron has a perfectly flat back which makes it excellent for setting in jewelry as is. This particular diamond is 0.63 carats, but because it has been sawn, appears in a piece jewelry as a much larger stone. It is approximately 6mm in length and 4mm in width, the type of width and length that would be seen in a rough diamond that is twice the carat size!

In the manufacturing process, a sawn diamond is then cut into a rough round shape if cutting into a round brilliant or into a square if cutting into a princess shape, retaining as much of the original rough diamond as possible so as not to lose the carat weight. The top of the cut round brilliant or princess, or "table", is cut from the side of the diamond that was sawn, and the bottom of the cut round brilliant diamond, or the "culet" is cut from the pointed tip of the sawn diamond. In the cutting process, 50% off the weight of a rough diamond octahedron is typically retained when cutting into a round brilliant, and, amazingly, almost 90% of the octahedron's weight is retained when cutting into a princess cut. Here's a quick look at a round brilliant diamond diagram, image courtesy of Tiffany's.

Round brilliant diamond cut

Whether you are shopping for a rough diamond for setting as is in rough diamond jewelry or for cutting and polishing into a beautiful polished diamond, an octahedron is an excellent choice. Browse our collection of rough diamond octahedrons here, or, as always, please feel free to be in touch with one of our rough diamond specialists, we would be happy to assist you. You can email us at or call us directly at 1-415-841-2747 . We look forward to working with you to match your exact rough diamond needs!

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