I had quite a lot of fun last week cutting my samples for thin-sections. Just imagine: a screaming saw going through the rock like butter, a diamond-coated blade sparkling against the strong quartzite, cold water splashing all over the face and dripping onto the shoes, a fearless girl daring her fingers for the cause of science… A theme for an action movie, isn’t it? Oh, just a regular day for a geologist.
A fully equipped lab geologist
Anyway, the rocks I sawed last week come from Australian and New Zealand’s shear zones which I will try to understand during the few following weeks. This time my task was to cut 2×3 cm large pieces out of them which we can send to a thin-section laboratory for further preparation. There they will be polished, glued to small slides of glass and grinded so thin that light can shine through (normally it is about 0.03 mm in thickness).
Samples ready to send out
The fancy little things at the end we call “thin sections” and they are extremely useful for geologists. By using an optical geological microscope we can precisely determine the minerals in the rock, their characteristics and arrangement. That provides a huge amount of information about the Earth’s history. We can infer how chemical reactions occurred, what deformation mechanisms where acting and in what kind of processes the particular rock was formed.
By using the techniques of electron microscopy we can go even further, down to an atomic level, and determine a precise chemical composition of even tiny spots in the section, as well as to find out exact crystallographic structure, defects and mis-orientations on a sub-grain scale.
It is funny how some years ago when I decided to be a geologist, I was looking on plate tectonics, large scale structural geology, determined if I will do something, I will do something big. And look where I ended up – doing microscopy. However this is not as contradictory to my megalomaniacal ambitions, as it may seem. When you think about it, everything what happens on large scale is eventually governed by these very subtle grain-scale processes. Therefore to understand a mountain belt you have to understand a thin-section.