This week's resource is a "virtual field trip" to a butte located in central Montana. Crown Butte is a laccolith that formed over 70 million years ago, and has been exposed by erosion. The butte and surrounding area feature examples of the following: columnar jointing, igneous rock in layers (layered igneous complex), a beautiful porphyry, lateral dikes, and a nearby extinct volcano. The photo on the right shows the porphyry that Crown Butte is made of. The large augite crystals formed before the molten rock moved from the magma chamber into the laccolith.
For a short preview, watch the PowerPoint presentation below, and then CLICK HERE to access the "virtual field trip". Here is the WORKSHEET (pdf file) that students will do as they use the web site. Another version of the worksheet is also available on the web site.