This title surely is not a phrase you see every day, but the phenomenon is perhaps one you’ve seen. The most noticeable diabase dikes I have encountered have been in the Tetons of Wyoming (think Mount Moran) and on the Schoodic Peninsula in Acadia National Park.
These wide, black stripes of rock formed as magma cooled and filled in the cracks within magma that had cooled previously. The difference in mineral composition between the magma that cooled first and the magma that cooled later created such distinct differences in color. Diabase is also softer than the surrounding granite so it erodes quicker and creates interesting cracks in the landscape.
Next time you’re hiking in a rocky area, look for these black dikes on the landscape!