Amudikha River, Nizhnyaya Tunguska River Basin, Evenkiysky District, Krasnoyarsk Krai, Russiai

Regional Level Types
Amudikha River	River
Nizhnyaya Tunguska River Basin	Basin
Evenkiysky District	District
Krasnoyarsk Krai	Krai
Russia	Country

A basalt area containing excellent zeolites, but rarely seen in collections. Many were collected by a Fersman Museum expedition to Siberia in the 1990s and brought to the west for sale.

The zeolite occurrences are located in altered basalts outcropping along the middle course of the Amudikha River, a right tributary of Yaktali River (река Яктали), about 350 km north of Tura village. This remote area was unsuccessfully explored for Iceland spar deposits in Soviet times.

Mordenite typically occurs as white fibrous crusts lining the cavities in altered basalts and constitutes the substratum on which crystals of later zeolites are grown. Little cavities can be completely filled with a loose mordenite "felt". Inclusions of fibrous mordenite in calcite crystals have been observed.

Stilbite-Ca is a ubiquitous mineral in the basalt cavities of the area; it typically forms yellow, thin tabular, prismatic crystals, often grouped into fascicled (bundled), sheaf-like aggregates, sometimes grown on a white mordenite "felt". Crystals can attain 7-8 cm in length, although sizes of 3-4 cm are more common.

After stilbite-Ca, heulandite-Ca is the most diffuse mineral in the area. It forms individual crystals, drusy aggregates and massive veinlets; its colour varies from yellowish to various shades of red and orange to almost colourless. Crystals can attain 7-8 cm in length, although their length usually does not exceed 3 cm.

Chabazite-Ca forms yellowish-grey individual and twinned rhombohedral crystals, often grown on fibrous mordenite and rarely on other zeolites or calcite crystals. Some huge crystals measuring up to 4.5 cm on edge have been found in 2012.

Thomsonite-Ca usually forms pinkish to yellowish to white spherulitic aggregates up to 2-2.5 cm across, grown on earlier zeolites. The mineral is not uniformly distributed in the area: abundant in some places, it is completely absent in others.

Analcime is a rare mineral in this area, although it has been abundantly found in one of the occurrences. It forms white crystals up to 2-3 cm in size.

Laumontite forms monomineralic veinlets and incrustations on the walls of the altered basalt cavities. Aggregates of laumontite crystals, up to 1-1.5 cm in length, are sometimes observed on other zeolites or calcite. The mineral easily dehydrates.

Calcite sometimes appears as optically clear Iceland spar, but more frequently is found as rather turbid white crystals, up to 2-3 cm, grown on zeolites.

Chalcopyrite is a rare mineral, found only in some places as tiny crystals (to 2 mm) included in heulandite-Ca crystals or disseminated on the surfaces of their faces.

Other Regions, Features and Areas containing this locality

References