Bill gave a really interesting talk on quartz and other forms of silica. The talk commenced with a general description of the elements that go to make up the earth's crust. Bill then delved more deeply into the chemical structure of silica and polymorphism and then into the different branches of the quartz family. This consists of, firstly, basic quartz types, for example Rock crystal, Rose Quartz and Citrine. Then there is amorphous quartz, including Opal and Obsidian. The Chalcedony branch includes Chrysophrase, Onyx, Heliotrope and the Agates. Most of these are fairly well known, but what are not quite so well known are some of the quartz/silica polymorphs. These are varieties that have been altered by heat or pressure or by both heat and pressure. These include minerals such as Keatite and Coesite. Silica also is present in many rock types, eg. Granite. These groups were then looked at in much more detail, accompanied by photographs of each mineral. Finally, the role of silica in technology was discussed from the use in quartz time-pieces to modern uses in nanotechnology.

Alongside the talk Bill brought along a large number of superb specimens for all to view.

The next talk will be on Wednesday 18th March, when guest speaker Kevin Voyce (Environment Agency) will give a talk entitled: “Strategic Ground Water Management”