The Journal is published by the Nature Conservation Agency of the Czech Republic in cooperation with the Cave Administration of the Czech Republic, the Krkonoše Mts. National Park Administration, the Bohemian Forest Mts. National Park Administration, the Podyjí National Park Administration and the The Bohemian Switzerland National Park Administration. It has been published since 1946.
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Nature Conservation 4/2008 — 19. 8. 2008 — Research, Surveys and Data Management
The Finding of the Opal in the Borgio Verezzi Cave
The Cave Administration of the Czech Republic staff members carried out mineralogical survey in the Italian Borgio Verezzi Cave.
Using the portable ultraviolet (UV) lamp with shortwave radiation (wavelength of 254 nm) they found opal in cave ornaments. The mineral was found in the cave for the first time. Nevertheless, opal is present in some karst ornament types. But there was a common pattern for each site where opal was found: all of them are macroscopically dry. Therefore, the author suggests that opal accumulation can be explained by the following mechanism. At some sites in the cave, slight amounts of solutions come out. Due to these slight amounts, water is totally evaporated there. In the vicinity of water provision inlet canals, the total mineral volume is deposited. Erosion processes on the surface or just in the rock, from which the solutions come out are supposed to be the SiO2 source for opal forming. In some cases, opal can be formed by releasing from clay minerals in the sediments. The karst ornaments containing opal found is among the youngest generations of the karst ornaments in the cave and it is even possible that opal has been recently formed in some cases.