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The Grove Hotel and Century Link Arena are located at the southeast corner of the Grove Plaza. The exterior walls of this building consist of an igneous rock know as granite. This particular granite is sold commercially under the name “Baltic Brown”, and is a popular material choice for both buildings and kitchen countertops. This granite comes from a magma intrusion known as the Wilborg Batholith in southern Finland. It is about 1.6 billion years old.

A close up visual scan of the walls reveals the same minerals observed at the Wells Fargo Building, including pink potassium feldspar, light-gray quartz, white plagioclase feldspar, Black biotite flakes, and needle like crystals of greenish-Black amphibole. However, there is clearly something different about this granite when compared to the Town Mountain Granite. This type of granite is known as “rapakivi” granite. Notice that the pink potassium feldspar crystals are not rectangular, but instead form oval or circular shapes. In addition these crystals are rimmed with a different type of mineral, a grayish plagioclase feldspar. This is interesting, and paradoxical because according to Bowen’s predicted sequence of crystallization, grayish plagioclase feldspar should crystallize out of the molten magma at a higher temperature and therefore before pink potassium feldspar. Yet in this rapakivi granite the opposite crystallization pattern is observed. The pink potassium feldspar is surrounded by the grayish plagioclase feldspar which mean that the grayish plagioclase feldspar must have crystallized after the pink potassium feldspar. To date, geologists have been unable to provide a satisfactory explanation for the paradoxical pattern exhibited by rapakivi granite.

Wilsey, Shawn. Geology Underfoot in Southern Idaho. Edition 1st. Mountain Press, 2017.