



Photographer: Baptiste Journaux

Summary Author: Baptiste Journaux

The photo above shows an outcrop with pegmatite found near Olary, South Australia. Pegmatite is an igneous deposit that often contains quite large crystals. The rock around the pegmatite is a mica-schist derived from ancient marine sediments deposited perhaps 1,700 million years ago. Pegmatite forms as a result of the partial melting of continental crust during mountain belt collapse phases; in this case probably at the end of the Olarian Orogeny. Magma that formed during this episode migrated upward in fractures in metamorphic sediments, initially creating linear intrusions. Then another phase of compression occurred (most likely during the Delamerian Orogeny) deforming the previously strained schists and the pegmatite linear intrusion. The result of this complex history is shown here where the pegmatite rock had been twisted in an anticlockwise rotation. Note that the rock hammer and backpack (and my feet) are used for scale. Photo taken on September 12, 2009.

Photo details: Camera Maker: NIKON CORPORATION; Camera Model: NIKON D80; Focal Length: 17.0mm (35mm equivalent: 25mm); Aperture: f/2.8; Exposure Time: 0.0003 s (1/4000); ISO equiv: 400; Exposure Bias: none; Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Auto; Flash Fired: No; Color Space: sRGB