Precious stones

The areas of Turnov and Nová Paka have been renowned for the finds of precious stones (semi-precious stones) since medieval times. Their source rocks are Permian basalts (paleobasalts), often displaying amygdaloidal (melaphyre) structure, i.e., containing numerous vesicles.

These vesicles are remains after bubbles of volcanic gases, which could not escape to the atmosphere from superficially extruded, rapidly solidifying magma. They remained entrapped in the rock and were later penetrated by hot silica-laden fluids (a by-product of volcanic activity). Upon cooling, various forms (so-called varieties) of quartz crystallized from these fluids. Amygdules filled with finely crystalline chalcedony or agate are the most frequently encountered ones. Rock crystal, amethyst or smoky quartz are found in geodes, larger veins and fractures are filled with jasper. Orange-brown carnelian was also formed by precipitation from silica-laden fluids. Nevertheless, it is rather found in the form of nodules in clay-dominated sediments. In addition, unusual and rare asteroidal quartz has been reported from fractures in basalt on Strážník Hill. Precious stones from the Geopark have been known since the Middle Ages. In the past, they were commonly collected, processed and traded by the local people to add small earnings to their regular income. These stones can be now admired in many great mineral collections in the world.


Created 18.2.2020 14:55:27 - updated 28.2.2020 22:41:34 | read 888x | sprokesova
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