Tertiary igneous rocks

Unit: T 30

image TI-30b

columnar basalt
full-size image

Sub-vertical columnar jointing in basalt, looking down. The columns are bounded by planar cooling joints. These joints resulted from contraction of a magma which cooled relatively slowly because the flow was thick. In this view, the columns have polygonal cross sections.

Scale: hammer shaft is 30 cm long .

Grid reference: 914 405

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This page is maintained by Roger Suthren

Last Modified: 23 October, 2008