Beryl is one of many crystals that are found in granite and also in some metamorphic rocks (those that were once deep in mountains under great heat and pressure).

It comes in a six-sided crystal, sometimes of massive sizes. The largest beryl crystal ever mined was 18m long and 3.5m across, and weighed 380,000kg. This is the largest crystal of any kind ever found in the world.

Beryl is often found in the same places as tin, in the rocks close to what were magma chambers and that cooled to granite.

There are two clear gemstone varieties, aquamarine and emerald.

Aquamarine (whose colour is pale blue - the name means 'water of the sea') is beryl with extra iron in it. The largest aquamarine of gemstone quality weighed 110kg.

An emerald is a green beryl. The colour is due to the element chromium. The word comes from the Greek meaning 'green gemstone'.

Emeralds were mined in Ancient Egypt and that is one reason they were part of royal treasures. Emerald is much rarer than aquamarine.

Both aquamarine and emerald are used in jewellery. The colour of aquamarine fades in light over several years.