Homework Help: Science: Earth: Volcanic Rocks

Basalt is in very fine grains, contains plagioclase crystals and gas bubbles and isn usually a dark grey colour. Volcanoes that produce this rock can be found on ocean ridges. Volcanoes that produce this rock are called sheild volcanoes.

Rhyolite has fine grains, with a light colour and occurs in lava.

Andesite is between basalt and rhyolite, with a smaller amount of biotite. It is found in areas that have lots of basalt volcanic activity.

Pumice is of a frothy texture and mostly glass.

Tuff is the product of the rock tephra hardening.

Obsidian is semi-translucent, glass and of a dark colour.

Homework Help: Science: Earth

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