What Gives Opals Their Colour?

Intro

Opals are among the most captivating gemstones, admired by collectors worldwide and sought after by those searching for opals for sale in the UK from me at W.M Opals. Their dazzling play‑of‑colour sets them apart from other gems, with each stone revealing flashes of colour which range across the whole colour spectrum.

Understanding how opals form helps explain why black opals, white opals, and even rare opal fossils for sale are so unique. For enthusiasts interested in opal mining or collectors of cut opals, knowing the science behind their colour adds even more appreciation.

📽️ Watch Video For More

Watch below where I talk about all types of Opals in more detail.

🔬 The Secret Structure: Silica Spheres

Opal forms from a solution of silica and water. As the water evaporates, it leaves behind a tightly packed, ordered array of microscopic spheres of silica - think of them as tiny, perfectly uniform marbles stacked neatly inside the stone.

The key to the colour is the size and uniformity of these silica spheres and the spaces between them. This is why collectors searching for loose white opals or premium black opals for sale UK often notice such variation in colour intensity.

✨ Diffraction and Refraction: Creating the Rainbow

When white light enters the opal, it passes through this structure of spheres. The light waves interact with the stacked layers, causing them to diffract (bend and spread out) and then refract (bend) as they pass through.

Opal Mining UK

I am personally fascinated with opals, this led me to go out mining for opals myself. As my knowledge around the industry grew, so did my knowledge around their formation and brilliance.

This is the science behind the famous “play‑of‑colour” that makes Australian opals so desirable to collectors. For those who buy cut opals, this rainbow effect is often the deciding factor in choosing a stone.

Sphere Size and Colour

• Smallest spheres (0.1 micrometers): Diffract short wavelengths → blue and violet.
• Medium spheres (0.2 micrometers): Diffract medium wavelengths → green and yellow.
• Largest spheres (0.3 micrometers): Diffract long wavelengths → red and orange (the rarest colours, often seen in premium black opals).

Since opals rarely contain a single, uniform sphere size, you often see a brilliant flash of multiple colours as you move the stone. This is why opals can look so different depending on their internal structure.

Summary

It’s the precision of this microscopic architecture that makes opals a dazzling wonder of nature. Whether you’re a collector searching for opals for sale UK, exploring the opal mining industry, or simply curious about their science, understanding how opals get their colour helps explain why they remain one of the most captivating gemstones in the world.

I at W.M OPALS believe I provide any buyer with access to unique stones and can guarantee their origin.

Browse my full collection of opals for sale UK today and discover the beauty of nature’s most dazzling gemstone.