Amethyst

A very busy day today, and lots of time sitting/lying around in hospital, so I didn't have as much time to hunt for a good blip, so this is another rock from my collection. It usually sits on a window-sill in the front room! This is a cluster of amethyst crystals - a violet-blue variety of quartz, which is almost pure silica. Amethysts are formed in gas bubbles in a magma - as the bubbles cool a 'skin' is formed on the outside edge (you can just make out the sealed dark edge in this photograph - and the crystals grow inwards into the middle of the bubble. Sometimes the middle space is filled up, and (better still) when there is not enough liquid to fill the space these perfect crystals form. This is a tiny part of the edge of one large bubble - you can gauge the scale by comparison to the 2.5 cm two-penny coin.