The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



micalike minerals of the group of layered aluminum silicates, containing additional water and possibly oxonium (H3O+). Hydromicas are usually intermediate products of the phase transition of various micas to kaolin, montmorillonite, vermiculite, and chlorites. The most widespread hydromicas are illite, (K,H2O)Al2[(Al,Si)Si3O10]-(OH)2.nH2O; rectorite, (H2O,K)Al2[AlxSi4-xO10](OH)23H2O; glauconite, (K,H2O)(Fe,Mg,Al)2[(Al,Si)Si3O10]-(OH)2; and hydrobiotite, (K,H2O)(Mg,Fe3+)3[AlSi3O10]-(OH)2nH2O.

The transformation of mica into hydromica is accompanied by the consumption of alkalies and the replacement in the interlayer space by molecular water, probably oxonium, and also the introduction of water associated with cations into special additional layers. Hydromicas increase greatly in volume when heated, as a result of the widening of the intervals between packets by water that is boiling and being driven off. The formation of hydromicas is predominantly associated with the weathering and change of mica minerals in granites, pegmatites, and other rocks. They are also formed as products of the decomposition of aluminum silicates of marine deposits during diagenesis. Less frequently they are formed in low-temperature hydrothermal associations by changes in rock containing ore veins.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Phase compositions of montmorillonite containing clay minerals were as follows: 1--montmorillonite 30 %, kaolinite 35 %, hydromica 35 %, quartz--traces; 2--montmorillonite 60 %, kaolinite 10 %, hydromica, quartz, feldspar--traces; 3--montmorillonite 80 %, zeolite 15 %, hydromica 5 %.
In this group of samples the highest conversion of methylbutynol was observed for palygorskite, and the lowest for hydromica and H-ZSM-5.
Comparison of the catalytic ability of both groups of samples from Russian and Jordanian deposits gives a general sequence for values of MBOH conversion: palygorskite > kaolinite-R > zeolite-J > bentonite-J > hydromica > red kaolinite > H-ZSM-5 > white kaolinite > diatomite.
However, presence of montmorillonite and hydromica along with kaolinite in natural sample explains higher yield of acidic products.
In the case of hydromica the yield of acid and basic products was practically identical.
Among the whole studied alumosilicates the sample of kaolinite from Russian deposit, containing also 30 % of hydromica and 10 % of montmorillonite, provided relatively high conversion of MBOH, which, at the same time, did not exceed the one provided by palygorskite.