Friday 19th January

Eighteen members attended the first meeting of the year despite the wind and rain. The AGM was followed by a very interesting talk by Bill Bagley in which he gave an overview of the mineral calcite. Bill took us through the processes of formation including a short video clip of the rare type of volcano producing carbonatite i.e. Doinyo Lengai volcano in Tanzania. With photos he explained calcite's structure and colour variations. That the most common crystal forms are scalenohedra, and rhombohedra and calcite readily cleaves into rhombohedra. It may also occur as prismatic crystals. The crystals may be tabular, acicular, prismatic and platy. Calcite can occur as crystals, stalactitic, massive, earthy, as aggregates or in geodes. The colour of calcite can vary from colourless through white, yellow, brown, reddish, bluish to black. It is also one type of mineral that shows birefringence.

The talk, along with the numerous impressive specimens that Bill brought from his own collection made for a very interesting evening.

The next meeting will be on Wednesday 14th February when Dr. Geoff Steel will give a talk entitled “The Origin of Atoms”

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Druzy Quartz and Calcite 2.

Druzy Quartz and Calcite 2.

Dylife mine, Central Wales Orefield. Detail from Druzy Quartz and Calcite 1. Although the deposits are very small, the cleavage and rhombohedral structure of the Calcite is well observed.
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The Silurian

Issue  Front Cover

The Silurian Issue 4 - January 2018

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We have also published a number of other resources.

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