Aegirite


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aegirite

[′ā·gə‚rīt]
(mineralogy)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Aegirite

 

(from Aegir, the Scandinavian god of the sea), also aegirine, a rock-forming mineral, a silicate of the group of monoclinic pyroxenes, with the chemical composition NaFe[Si2O6]. It contains admixtures of Mn, Zn, Ti, Nb, Zr, and V. As a result of the isomorphism Na+ ⇆ Ca2+ accompanied by the replacement of Fe3+ by (Mg, Fe)2+ or Si4+ by Al3+, transitions are observed to aegirite-diopside, aegirite-hedenbergite, and aegirite-augite.

Aegirite occurs in the form of elongated tabular, columnar, or acicular crystals, radiated and fibrous (”mermaid hair”) concretions, and sometimes spherulites. The color ranges from green to greenish black; sometimes the mineral is almost colorless. Aegirite has a vitreous luster, a hardness of 5.5–6 on Mohs’ scale, and a density of 3,400–3,600 kg/m3.

Aegirite is a typical mineral in alkali rocks and associated pegmatites; it is also characteristic of zones of alkaline metasomatism that develop after various intrusive and sedimentary-metamorphic rocks (gneisses, schists, and ferruginous quartzites). In agpaitic nepheline syenites it is found together with nepheline, orthoclase, eudialite, and apatite. In alkali granites it occurs with albite, riebeckite-arfvedsonite, and zircon. In zones of alkaline metasomatism it is found together with albite, hematite, and pyrochlore. Aegirite alters to chlorite, hematite, and limonite.

A. I. GINZBURG

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.