Tonalite

The name and its history

Gerhard vom Rath (1864), according to geological historical accounts · 1864 (secondary attestation)

What does the word literally mean?

Literal naming sense: rock of Tonale. Immediate language/formation: German petrological coinage from Tonale Pass. The deeper etymology of Tonale is not established by the rock-name source.

What did the original author mean?

Vom Rath used the Tonale geographical association for a plagioclase-rich granitoid of the Adamello region.

Why was the name needed?

The Alpine plutons required a name for a rock not adequately described by the broad contemporary labels granite and diorite.

What evidence supported the original concept?

Field specimens and petrographic identification in the Tonale–Adamello rocks.

How has geology changed the concept?

The international modal field can describe tonalites anywhere; the type district does not delimit the class.

Further historical context

Vom Rath used the Tonale geographical association for a plagioclase-rich granitoid of the Adamello region.

The Alpine plutons required a name for a rock not adequately described by the broad contemporary labels granite and diorite.

Field specimens and petrographic identification in the Tonale–Adamello rocks.

The international modal field can describe tonalites anywhere; the type district does not delimit the class.

Related names

Granodiorite · Trondhjemite · Plagioclase · QAPF classification · Diorite

Sources

1. Hochschule München, Geological collection: Tonalites and diorites — Names Gerhard vom Rath, 1864, and Tonale Pass
2. BGS, Rock Classification Scheme — Modern descriptive rock-naming principles and definitions
3. USGS, Lithologic classification of geologic map units — Modal definitions and named plutonic-rock categories
4. IUGS / Le Maitre et al. (2002), Igneous Rocks: A Classification and Glossary of Terms, ch. 3 — Authoritative IUGS rock-name history and bibliographic attributions