11 May 2026
An Incredible Discovery of a Triangular Iron-Bearing Inclusion Within a Natural Diamond!
A striking triangular feature was observed in a natural diamond, captured under the microscope in our London laboratory. Inclusions like this are far more than blemishes: they are a record of the extraordinary conditions under which the crystal grew, and they are one of the most powerful tools we have for confirming that a stone is natural.
Table of ContentsAn Incredible Discovery of a Triangular Iron-Bearing Inclusion Within a Natural Diamond!What We Saw Under the MicroscopeWhy Is the Inclusion Triangular?What Causes the Orangey-Brown Colour?Why Inclusions Matter in a Natural DiamondOther Hidden Wonders Inside DiamondsHave Your Natural Diamond Examined
What We Saw Under the Microscope
At first glance the stone looked like any other well-cut diamond. At 40x magnification, however, a sharply defined, orangey-brown triangle appeared beneath the table facet, its three sides perfectly straight and its colour in vivid contrast to the colourless crystal around it. The image above shows exactly what our gemmologist saw through the eyepiece.
Why Is the Inclusion Triangular?
This triangle reflects the diamond’s natural octahedral growth structure within its cubic crystal system. A diamond octahedron is made up of eight triangular faces, and as the crystal grew layer by layer, anything trapped between those layers took on the same three-sided outline. Triangular shapes are therefore a signature of natural growth, seen in features such as trigons on rough crystal faces and in the geometry of many included crystals.
Laboratory-grown diamonds grow in a very different way. HPHT (high pressure, high temperature) crystals develop cube and octahedral faces together, while CVD (chemical vapour deposition) material grows in flat layers, so their inclusions and growth patterns look distinctly different under magnification.
What Causes the Orangey-Brown Colour?
The orangey-brown colour is caused by a trapped iron-bearing mineral inclusion that has naturally altered over time, creating its distinctive rusty appearance instead of remaining clear. Just as iron rusts when exposed to air and moisture, iron-rich minerals trapped in a diamond can oxidise along tiny fractures that reach the surface, staining the feature a warm brown.
Iron-bearing minerals are relatively common guests inside a natural diamond. Garnet, chromite, olivine and various sulphides are all found as inclusions and, because they formed at the same time as their host 150 kilometres or more below the Earth’s surface, they give geologists a rare glimpse of the deep mantle.
Why Inclusions Matter in a Natural Diamond
Proof of origin: included crystals and growth features confirm the stone is natural rather than laboratory grown.
Clarity grading: the size, number, position and visibility of inclusions determine the clarity grade on a report, from Flawless down to Included.
Identification: an inclusion is a fingerprint that is unique to one stone, which is how a diamond can be matched to its report years later.
Durability: large inclusions that reach the surface or sit near the girdle can make a stone more vulnerable to chipping.
The Gemological Institute of America (GIA) grades clarity on the same 11-grade scale we use at E.D.R, and an inclusion like this one would be plotted on the stone’s clarity diagram.
Other Hidden Wonders Inside Diamonds
This is just one of the many hidden wonders that can exist within diamonds. Clouds of microscopic pinpoints, feathers that flash like tiny mirrors, green garnets, and even smaller diamonds trapped inside larger ones have all passed across our microscope stage. Many natural stones also reveal a hidden glow under ultraviolet light, which we explore in our article on fluorescence in diamonds.
If you are curious about how inclusions shape value, our guides to the 4Cs and to diamond shape and cut explain how clarity fits alongside colour, cut and carat weight, and how a laboratory-grown diamond is separated from a natural one.
Have Your Natural Diamond Examined
Got a question about any of your diamonds? Whether you want confirmation that a stone is natural, a full grading report, or simply to see what is hiding inside your own gem, get in touch today and we’ll be happy to assist you in finding the right solution for you!