BLOG 8: Processing the Rocks

By Chris Meagher

One of the major goals of this voyage is to identify the age of the seamounts in the Tasman Sea. To do this the scientific team used a rock dredge to collect samples from seamounts many kilometres under the water surface.  Dredging material from kilometres under the ocean can be more art than science, so the moment when the dredge basket is raised up onto the ship’s deck is always fraught with tension.

For the first dredge of the voyage we were in luck and the basket full of rocks was lowered to the deck. Once the all clear was given the team began poring over the samples looking for early clues as to their origin.

A number of the rocks contained biological material and these were quickly examined and photographed. As the main focus of this trip was geology we were not permitted to keep any rocks containing live organisms so these were quickly returned to the ocean.

The volcanoes which created these seamounts erupted around 30 – 50 million years ago so many of the rocks have been significantly altered. The most obvious sign of this is thick crusts of black manganese which builds up on the rocks over millions of years. To properly identify and date the rocks they were cut with the rock saw to reveal the original or “fresh” rock in the centre.

After cutting the rocks were moved to the wet lab where teams of geologists examined each rock in detail using hydrochloric acid to test for remnant coral or shells, magnets to test for metallic content and microscopes to identify minute crystals such as feldspar.

The rocks were then meticulously catalogued, photographed and stored ready to be further analysed and dated back on shore.