Date: Pre-Cambrian Era (1.6 billion years old)
Description: Diorite is an intrusive igneous rock, meaning it is formed by magma deep in the earth before it erupts from a volcano. Though relatively rare worldwide, it is fairly abundant in the Siouxland region because of the heavy volcanic activity that was present in region during Pre-Cambrian times. The diorite samples we have are some of the oldest rocks ever found in this region. This sample was found in Lein Quarry in Sioux Falls, SD.
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