Dike in a granite
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This rock is a granite that solidified between 350 and 320 million years ago. More than 120 million years later, molten basaltic rock forced its way upward through a fracture to form a gray-black dike in the granite. Note the difference between the fine-grained margins of the dike, which cooled quickly against the cold granite, and its coarser-grained interior, in which slower cooling allowed crystals to grow larger.
Provided by Royalty Granite, Elberton, Georgia
Topic: Earth Science
Subtopic: Earth Formation/Evolution
Keywords: Dikes (Geology), Granite, Magmas