Gneiss and gabbro

Figure 7. Both types of rock are visible in this photograph. (Photograph by Dirk Frankenberg. More about the photograph)

Figure 7 shows a close-up of the contact between the gneiss and the intruded gabbro. The gneiss is at the top. It is light colored and its surface is pocked by erosion. The gabbro is on the bottom, is darker and has a much smoother surface. The knife (shown for scale) is three inches long. The sharp contact between the two rock types shows that little mixing occurred when the molten gabbro was forced into cracks in the gneiss, but the lighter color of the gneiss near the contact suggests that some additional metamorphosis of the gneiss may have occurred near the contact zone.

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