dyke is a forceful injection structure (generally shown by igneous rocks, but not restricted) in the country rocks. for this, their orientation is different from the country rocks. They are often identified by their colour contrast from the surrounding rocks ...for example a dyke of dolerite intruding in a granite body. But when the composition and as a result, the colour of the dykes are similar to the country rocks, they are difficult to discern. we need to closely see them in field. In the photograph below, we have seen dykes in Deccan basalts where they are standing like long walls; the surrounding rocks have been more weathered owing to their mafic, coarse-grained nature and certainly old age than the dykes.
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