What is Lustre?
Lustre Reflection or Scattering of Light
Lustre is a description of the way light interacts with the surface of a crystal rock or mineral. It's the reflection or scattering of light from the surface of the stone. Lustre describes the stone’s appearance in reflected light.
The words used to describe different types of lustre include;
Rocks minerals and gemstones with a vitreous lustre reflect light in a similar way to glass. Vitreous is one of the most common types of lustre. It's often present in stones that are translucent or transparent.
For a stone to exhibit this type of lustre it needs to have a relatively smooth surface and high reflectivity.
Lustre is often confused for brilliance but the two are not the same. Lustre is the way light is reflected off the surface of a stone. Brilliance is the way it reflects light from within the stone. Brilliance can only be seen in highly translucent to transparent gemstones.
One of the main reasons for faceting a gemstone is to maximise brilliance. The way a stone is cut can affect brilliance.
Polishing will almost always improve lustre whether a stone is transparent, translucent or opaque.
There are two broad types of lustre, metallic and non-metallic. All crystals rocks and minerals fall into one category or the other.
Metals have a metallic lustre whilst most other rocks and minerals are non-metallic. Two exceptions are the minerals hematite and pyrite.
'Lustre' comes from the Latin 'lux' meaning 'light'. In addition to those already mentioned, other types of lustre include pearly, silky, resinous, earthy and adamantine.