Photographer: Calvin J. Hamilton Copyright: © 2006 Calvin J. Hamilton Date Added: 2006/12/30 Location: Kunia, Oahu, Hawaii

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• Basalt

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Caption

This sample of picritic basalt was made at a high temperature of 1200°C (2200°F) about 2 miles underground in the magma chamber of the Ko'olau volcano. The high temperature allowed the large olivine crystals to form. The crystals grew very slowly for years while underground. The blade-like black and white plagioclase crystals formed during and shortly after the eruption of the magma. The rock dates to 2.5 million years ago.