Geologists in Africa have found economically valuable concentrations of chromite (the principal ore of chromium) that formed by gravity settling in thick mafic sills. In the same area of Africa, there are also mafic lava flows that look very much like the sills but which contain none of the valuable minerals. You have been hired as a geologic consultant by an investment firm that is considering purchasing the mineral rights for the mountain that includes the sills. The firm specifically needs to know whether the mafic igneous rock (in the photograph below) is a sill (i. e, intrusive) and therefore worth the cost of explora- tion or a lava-flow (ie, extrusive) and therefore not worth a penny. Required:
What metamorphic evidence would you look for that would distinguish the two possibilities?