Minerals and light

A light bulb Take a mineral and hold it up to a light - what can you see? One of the first things you should notice is whether you can see through it or not.

What can you see when you hold your mineral up to a light?

How to judge your mineral
Hold your mineral up to the light and choose a thin section, an edge or corner. You should be able to judge whether your mineral is transparent, translucent, or opaque. This property is a useful tool to help you to identify your collection.

Most minerals are transparent (you can see right through them, like plain window glass), or translucent (more like frosted glass). Tiny bubbles of gas or other impurities trapped inside a crystal can make a transparent mineral look translucent. Metals like gold and silver, and some minerals containing metals, are opaque - you cannot see though them at all.

In the pictures below, the calcite is transparent, while the gypsum is translucent and the gold is opaque.

Calcite Gypsum Gold

Judging how a mineral transmits light is a good step in identifying your specimen.

Ernest the mineral detective To find out about minerals you should Take a closer look, and then find out about some of their properties...

Colour Light
Lustre Streak
Crystal shape Hardness
Cleavage and fracture Heaviness
Other tests What we have learnt

Return to the Detectives homepage, or finish by playing Mineral mastermind!