At the Visitor Centre of Snæfellsjökull National Park, specimens of several different rock types found in Iceland are on display. Although Iceland is built predominantly of countless layers of basaltic lava, many other rock types also occur. Just as basalt differs from peridotite, which represents the Earth’s upper mantle, the other rock types have formed through different magmatic and geological processes.
In many cases, the cooling history of the magma is the most obvious factor controlling the final rock type. Rapid cooling, particularly beneath glaciers or in water, may produce volcanic glass and palagonite, while slow cooling beneath the surface allows coarse-grained rocks such as gabbro to crystallize. Rhyolite is much richer in silica (SiO₂) than basalt, and if rhyolitic magma cools extremely rapidly before crystals can form, it solidifies as obsidian.
This is a very informative exhibition and is highly recommended for anyone interested in Icelandic geology.
Magic Magma 