What is Diaphaneity?

Diaphaneity: How Much Light Can Pass Through

Diaphaneity is an optical property that describes how much light can pass through a material without being scattered or absorbed.

The word 'diaphaneity' originates from the Greek 'diaphanēs', meaning 'transparent' or 'to show through'. It combines the Greek roots 'dia', meaning 'through', and 'phaino', meaning 'to show' or 'to appear'.

Over time, the word 'diaphaneity' was adopted into the field of mineralogy and other scientific disciplines to describe the degree of transparency or translucency of minerals, gemstones, and other substances. So basically, how well a substance allows light to pass through.

A transparent material allows light to pass through with little or no scattering, allowing objects to be seen clearly. Glass is transparent.

Something translucent allows some light to pass through, but it's scattered or diffused. An object viewed through a translucent material can be seen but is blurred or obscured. An example is frosted glass.

Metal and wood are opaque, so no light can pass through.

The diaphaneity of a substance depends on its crystal structure, as well as impurities or inclusions.

Some translucent gemstones can initially appear to be opaque until they're held up towards light.

The degree of translucency in a mineral or gemstone can vary considerably. Agate can be virtually opaque to highly translucent.

Transparent and highly translucent gemstones tend to be faceted. Stones that are opaque or exhibit low translucence, are usually cut as cabochons.

Gemstones that exhibit optical phenomena such as chatoyance, play of colour, or asterism are also cut as cabochons because the dome-like shape enhances the effect.