CSM Rock Collection

Gabbro, IG09NR01
Location: Unknown

Description

Gabbro is the plutonic equivalent of basalt. Basaltic magma is the dominant type at tectonic spreading zones and volcanic hot spots. Basaltic rocks dominate the ocean floor as well as oceanic islands such as Hawaii and Iceland. On the continents, they are found in tectonic rift zones as well as hot spot related flood basalt provinces.

Hand specimen

Specimen size: 95 x 60 x 40 mm
The hand specimen displays a mixture of white and black crystals in nearly equal proportions. The overall colour is dark consistent with a mafic rock, and the grain sizes of the different minerals are rougly similar.

Field of view: 30 x 22mm
With a hand lens, it is possible to examine the two principal minerals. The white mineral has a prismatic shape and displays two good cleavages, the mineral is twinned and harder than steel. Although more difficult to see, the black mineral (which upon close examination appears to be brown) also has two directions of cleavage, the hardness is roughly equal to that of steel. The two directions of cleavage intersect at around 90º.

IG04AD01_ppl

Field of view: 30 x 22mm. This hand-lens view displays the shape, cleavage and twinning in the white mineral better. The

Thin section

Thin section in plane polarised light (full section)

Plane polarised light image. Geologists will be taught how to use the microscope during term 2.

Thin section in cross polarised light (full section)

Cross polarised light image. Geologists will be taught how to use the microscope during term 2.