Igneous rocks of the Highwood Mountains, Montana: Part VI. Mineralogy

GSA Bulletin
By: , and 



The minerals of the igneous rocks of the Highwood Mountains are described. The primary hornblende of the quartz latites is basaltic and it has been partly replaced by a common green hornblende. Hornblende is rare in the alkalic rocks. Augite is an abundant mineral of the alkalic rocks; in the syenites it contains some acmite, especially on the borders of the crystals. Aegirite is a common metamorphic mineral. The olivine of the shonkinites contains from 12 to 22 mol per cent of fayalite, that of the syenite from Square Butte 50 per cent. Monticellite twinned into trillings on (031) is an abundant mineral in one small intrusive body. In the alkalic rocks barium sanidine is abundant and plagioclase rare; leucite, primary analcime, and pseudoleucite are common and sodalite rare. Natrolite, thomsonite, and other zeolites are widespread and very abundant.

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Publication type Article
Publication Subtype Journal Article
Title Igneous rocks of the Highwood Mountains, Montana: Part VI. Mineralogy
Series title GSA Bulletin
DOI 10.1130/GSAB-52-1841
Volume 52
Issue 12
Year Published 1941
Language English
Publisher Geological Society of America
Description 16 p.
First page 1841
Last page 1856
Country United States
State Montana
Other Geospatial Highwood Mountains
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