Agates of the Upper Płóczek, Poland

Photographs

Nothing occurs in agates, jaspers, opals, or lithophysae (amygdules, geodes, thundereggs), or vein agates by accident. Structures form due to specific geologic conditions, and inclusions form due to precise conditions of geochemistry. Reactions of one mineral making another occur all the time in these rocks. When we decipher what happened to a specimen from its structure and inclusions, what we see tells us much more that silica chemistry itself can.

Overall, the Polish amygdules shown here are dominated by chlorite reaction chemistry that formed the green vermicular and curl structures. From the type of chlorite present, iron compounds, manganese, and clays are released into the structure interior, providing the green, reds, yellow, blues, and whites seen. While very beautiful, the Polish amygdules show a very narrow range of geologic conditions that formed them.

It is also seen that the green “prasiolite” presumed to be a green quartz from predecessor amethyst exposed to high temperature, is probably a beta-quartz mixed with alpha-quartz. This beta-quartz indicates that those amygdules were exposed to high temperatures, but while prasiolite forms at about 400 C, beta-quartz forms at 574 C. The author proposes that beta-quartz and beta-moganite can be identified with infrared spectroscopy. Beta-quartz is found in prasiolites mixed with alpha-quartz, while beta-moganite that forms at 354 C, is not.

All of the interpretation sections of this text, including the photos that follow, where added by Donald Kasper, based on 10 years work studying the inclusions and structures of the agates in the Southwestern United States. Later, he applied his work to classify the Lake Superior agates (also metamorphically exposed), and here, the Polish agates.

Donald Kasper, 2016