Rock history
When magma rises from the Earth's mantle, it can either solidify inside the crust, like gabbro, or slither all the way to the surface, like the lava-variety of gabbro, aka basalt. Once the magma has crystallised in the crust and formed a so-called intrusion, it can either just sit there and slowly be unroofed by erosion of overlying rocks, or it can be subjected to tectonic events such as being pressed deeper down by mountain-building or shooting up by exhumation.
In SW Sweden, the rocks have been subjected to more than one tectonic event;
in fact, the deformations are so complex there rages a decades-long debate in
academia over what really happened, and how, and when. Aspiring geologists are
taken to locales that show initial sedimentation, folding, refolding of the folds,
perhaps yet another folding, veins and shears cutting some folds but being
folded by younger folds...
Minerals can say something about what has happened to the rock: Certain assemblages of minerals in, say, a gabbro, are typical of various pressure and temperature (P-T) regimes, also known as metamorphic facies. Low-pressure minerals forming reaction rims around high-pressure minerals tell us this rock came from deep down and then was raised and stayed at lower-pressure conditions long enough for new minerals to form. Minerals are stable at certain P-T conditions and unstable at others, and when conditions change they try to turn into other minerals, i.e. to re-equilibrate, exchanging elements according to experimentally derived reactions.
This is what I have done, going through these three steps: ordinary microscope work, SEM-EDS, and TWQ...