Agate – Rasovka (Prosec pod Jestedem), CZ
Locality: Rasovka (Prosec pod Jestedem), Czech republic
Weight: 424g
Dimensions: 11,5 x 6 x 4 cm
Polished on one side
| Category: | Rasovka |
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Agate, Amethyst, Quartz – Prosec pod Jestedem
A unique occurrence of agates was discovered in occasional excavations near Proseč pod Ještědem, approximately 5 km southwest of Liberec. The site was located about 300 metres northeast of Proseč, to the right of the road leading to Rašovka on the southwest slope of the Rašovský Ridge, formed by the Hodkovice Permo-Carboniferous, specifically the upper “melaphyre” cover of the 3rd phase of the local Permian volcanism, which consists of melaphyre amygdaloids, palaeorhyolites and their tuffs occurring along the Lusatian fault.
The best finds originate from collections from 2004 to 2007. More recently, up to 30 cm large fillings and geodes have been found on the southwest slope of the Rašovský Ridge in weathered melaphyres, with the larger ones formed by a grey chalcedony rim with sparse agate banding. Their central, often dominant part is filled with whitish crystalline quartz and its varieties (rock crystal, amethyst and smoky quartz).
These coloured varieties of quartz often alternate, forming layered zones (whitish quartz, amethyst or amethyst transitioning into smoky quartz, etc.). On smaller specimens, the denser and sometimes pleasantly pastel-coloured agate pattern is more prominent.
The local finds of beautiful quartz geodes and agates rank among the top-quality specimens, as do the very fine local jashttps://www.peltramminerals.com/en/jasperpers. The surface of the “nodules” is not formed by grey-green chlorite “delessite” as in other localities, but mostly by a fine-grained, brick-red crust composed of a mixture of zeolites, with the red edges of the nodules formed by the zeolite mordenite.
Mordenite
Mordenite is a calcium–aluminium silicate from the zeolite group. It forms columnar crystals, needle-like to fibrous radial aggregates, or may occur massive. It is colourless, white, pinkish or flesh-pink.
No new finds of some of the highest-quality agates from the Czech Republic have been appearing from this locality. Therefore, they retain their value and will likely continue to rise.