subalkaline rock

geology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

Subalkaline rocks are a classification of igneous rocks characterized by their chemical composition, specifically their alkali (sodium and potassium oxide) and silica content. They are distinct from alkaline rocks, which have a higher proportion of alkalies and can form alkaline minerals.12

Subalkaline rocks are further divided into two groups: the tholeiitic series (iron-rich) and the calc-alkalic series (iron-poor). The tholeiitic series is commonly found along oceanic ridges, while the calc-alkalic series is characteristic of volcanic regions on continental margins. Chemically, subalkaline rocks are saturated with silica, meaning they can contain normative minerals like quartz and orthopyroxene.13

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

igneous rock
Classification of volcanic and hypabyssal rocks
The subalkaline rocks have two divisions based mainly on the iron content, with the iron-rich group called the tholeiitic series and the iron-poor group called calc-alkalic. The former group is most commonly found along the oceanic ridges and on the ocean floor; the latter group is…
Read More
The subalkaline rocks have two divisions based mainly on the iron content, with the iron-rich group called the tholeiitic series and the iron-poor group called calc-alkalic. The former group is most commonly found along the oceanic ridges and on the ocean floor; the latter group is…
Read More