The Gonabad Thunder's Eggs
Gonabad thunder's egg field, Gonabad, South Khorassan Province
Gonabad thunder’s egg field situated in 12km north-northwest of Gonabad city, in South Khorassan province, east of Iran. The geology of area composed of a vast volcanic sequence with rhyodacitic to andesite-basaltic composition which shows a continental volcanism with acidic to intermediate term. This volcanic sequence is late to early-middle Eocene in age based on K-Ar dating which has been done during geological surveying in 1:250000 scale and revealed 51.6 to 54.8 MY age for this volcanic rocks.
The intense weathered hills which covered with broken volcanic rocks formed the common sight of this area. Surface of the hills is covered with many loose nodules of thunder’s egg which mostly broken. They are purple to red in color and have a mean diameter between 5 to more than 40 cm. Some exploratory diggings have been done for exploration agate reservoirs by Gowhartarashan-e-Shargh Company. It is not so far from exception that their exploratory operation had not hopeful results. Nodules are mostly filled with quartz crystals and are thunder’s egg geodes which are far from their exception.
Most of nodules basically are filled with quartz crystals, so called “frozen” and have not commercial value. The others are mostly thunder’s egg geodes with little central void. They are look like “Palumas geodes” which is one of the famous types of Mexican T.E geodes which come from Chihuahua province in Northern Mexico. But real T.Es which full filled with chalcedony with show circular to horizontal banding are too rare in Gonabad nodules. These T.Es are filled with pale blue chalcedony and show weak banding.
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