Andesite, Dacite, and Rhyolite

What is Enstatite?

A variation of orthopyroxene and the magnesium end-member of orthopyroxene.

What characterizes Augite?

A variation of clinopyroxene and an intermediate member of the diopside-hedenbergite series.

What is Andesite?

A fine-grained, usually mesocratic igneous rock consisting essentially of plagioclase and one or more mafic minerals.

What type of volcanic rock is Andesite?

The second most abundant volcanic rock type.

What are the characteristics of Dacite?

A fine-grained usually leucocratic igneous rock consisting essentially of sodic plagioclase and quartz.

What denotes the presence of alkali feldspar in Dacite?

If present, it is subordinate to plagioclase.

What is Rhyolite composed of?

Quartz and alkali feldspar, usually as phenocrysts set in a glassy microcrystalline groundmass.

How does Dacite differ from Andesite?

Dacite has abundant quartz while Andesite has dominant mafic minerals.

What is the main difference between Dacite and Rhyolite?

Dacite has dominance of alkali feldspar in plagioclase, whereas Rhyolite has sodium-rich plagioclase and alkali feldspar greater than plagioclase.

What are Boninites?

Fine-grained igneous rocks containing abundant opx phenocrysts and microphenocrysts but no plagioclase.

What is significant about Boninites?

High Mg-andesite from the Bonin Islands, Japan with SiO2 > 52 wt%.

What are the products of fractional crystallization of basaltic magmas?

Intermediate and acidic magmas.

Where is there an abundance of ADR?

In mature island continental arcs, possibly contributed by sialic continental crust.

What is commonly associated with arc magmatism?

Significant volumes of ADR in large igneous provinces and rift zones.

From where have ADR been reported?

Oceanic spreading centers.