GeoCo Rocks

Pentlandite says:

well you already know about foliated and non foliated textures, depending on the rock in thin part you would look for index minerals (sillimanite, andalusite, cordeirite just to name a few), the %’s of minerals in the part, look for bent or glide twinning in your “Plagioclase” (albite-anorthite), if you see something like amphibole and pyroxene in the same rock, you probably had some setback of bowens reaction run caused by dyhydration. If you have a sedementary rock you would look for things that would indicate a high amount of pressure; for example a 3 point contact point between 3 quartz grains, or look at the quartz grains cementing together (looks kind of like a shadow) you would still see foliation of biotite and muscovite and whatever else decides to foliate. hand samples can be a bit more trying, just look for textures, some are very simple where as others can only be identified under a microscope.