STORIES - What determines the colour of a gemstone?

When you look at an emerald ring or a sapphire blue pendant, you might wonder: where does this colour come from? What makes a ruby intensely red, while a diamond remains sparklingly colourless?

A gemstone's colour is no accident. It is a game of chemistry, light and physics that takes place deep beneath the earth's surface. In this blog, we dive into the fascinating science behind gemstone colours.

The role of chemical elements, the colour-makers

Gemstones are made up of certain substances, but their colour often comes from small amounts of other metals. These are called chromophores. They act as a kind of dye that gives the gemstone its special hue.

·       Chromium gives ruby its fiery red and emerald its velvety green.

·       Iron gives deep blue sapphires or warm yellow tourmalines.

·       Manganese provides pink hues in rose quartz or spessartien garnet.

·       Titanium and iron together? That makes sapphires sky blue.

What is interesting: some gemstones are actually colourless in their purest form. It is only when chromophores are present that colour emerges.

Crystal structure determines how the stone plays with light

The way atoms arrange themselves in a crystal structure affects how a gemstone interacts with light. That interaction determines which colours are absorbed, and which instead reflect or shine through the stone.

This structure also allows gemstones to exhibit special phenomena, such as:

·       Pleochroism: the stone shows different colours from different angles (e.g. tanzanite).

·       Asterism: star patterns visible in ruby or sapphire, due to inclusions that reflect light.

Light absorption: what you see is what remains

When white light hits a gemstone, the stone absorbs certain wavelengths (colours) of that light. The colours that are not absorbed are the colours we see.

For example: a ruby absorbs blue and green light, and reflects red light. Therefore, we see ruby as red.

Heating and treatments

Some colours in gemstones can be enhanced or changed by heat or irradiation. These treatments are ancient and common in the jewellery world.

·       Heating of sapphire: deepens the blue.

·       Irradiation of topaz: changes colourless topaz into intense blue.

As long as this is communicated honestly, it remains an accepted usage in gemology.

Colour is character

A gemstone's colour tells a story. It is the result of millions of years of geological activity, a touch of chemistry and the unique interaction with light. Every stone is different, even within the same family.

Want to choose a stone that really suits you? Don't just look at the colour you like, but feel what attracts you. byJACKY is happy to help you make that choice.