A well crystallized example of Jarosite (a Potassium Iron basic Sulphate). Although Jarosite is a widespread mineral, it seldom forms crystals of any note. One of the most well known locations for crystals of Jarosite is the mines of the Lavrion District in Greece. The crystal specimen we have comes from the mines around Agios Konstantinos. The Jarosite forming a sparkling brown druse of translucent well formed platy crystals to around 1mm. The crystals fill an elongated cavity at the centre of the specimen, in a hard Fe-oxide matrix. The specimen has many other cavities all over it also with Jarosite crystals. An interesting specimen from the very ancient (pre Roman) Lavrion mines.