Inclusions and durability

Almost every natural gemstone contains inclusions: tiny crystals, liquids, gas bubbles, needles or healed fractures that were trapped during growth or formed later. They are often seen as flaws, but first of all they are information.

Inclusions as a feature

Inclusions tell how and where a stone grew. Rutile needles in corundum, three-phase inclusions in emerald or growth tubes in tourmaline help the laboratory to identify the material, to separate natural from synthetic and sometimes to narrow down the origin. In emerald, inclusions are so characteristic that they are called the "jardin", the garden.

When inclusions affect durability

Not every inclusion is the same. For durability the following matter most:

• Type: open fractures or cleavage planes are more delicate than enclosed crystals
• Position: a feature near the girdle or a corner is more exposed than one in the centre
• Extent: the larger and the closer to the surface, the more likely pressure or heat can cause damage
• Filling: filled fractures are less visible but react to cleaning and heat

Hardness, toughness and cleavage

Hardness describes resistance to scratching, toughness the resistance to breaking. A diamond is extremely hard but can chip along its cleavage planes if struck. An emerald is hard enough, but less tough because of its inclusions. That is why a stone's suitability for jewellery worn every day depends on more than hardness alone.

Inclusions and beauty

Many inclusions are only visible with a loupe and barely affect appearance. Fine silk can even give a sapphire a soft glow. The question is not whether inclusions are present but whether they noticeably affect appearance or durability.

In brief

Inclusions are first of all information about a stone's formation and identity. For durability, their type, position, extent and any fillings matter. Knowing these features allows a stone to be assessed correctly, set appropriately and worn safely in everyday life.

At NOBILITH

The Academy shows typical inclusions of each species under the virtual microscope. A stone's dossier records the laboratory's observations. When a stone is reset, we point out sensitive areas so that the goldsmith can take them into account.

Sources

• Gübelin, E. and Koivula, J.: Photoatlas of Inclusions in Gemstones
• GIA: Gem Encyclopedia, inclusions and durability