Tertiary igneous rocks

Unit: IG 7

image TI-03

full-size image

A layered "gabbroic" rock. The mafic minerals are olivine and pyroxene, the felsic mineral is plagioclase. Note:

i) the concentration of mafic minerals at the base of each unit;

ii) the decrease in grain size upwards in the complete unit shown;

iii) the very sharp top to this unit. These features are typical of cumulate rocks, i.e. those thought to have formed by the successive accumulation and crystallisation of discrete crystal - magma units in a convecting magma chamber.

Scale: overall length of opened hand lens is 80 mm

Grid reference: 965 384

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Last Modified: 23 October, 2008