Shonkinite is an uncommon type of intrusive igneous rock found in Montana, Ontario, Canada, and the southeast Indonesian island Timor. The dominant materials that comprise the dark-colored rock are orthoclase feldspar and augite.

View a second image of Shonkinite

Many early geologists named rocks that were readily distinguishable from other types of rocks as soon as they were discovered. Often times these names were based upon the place where the rocks were first identified. Indeed, the term shonkinite derives from Shonkin, the Native American name for Montana’s Highwood Mountains, where this rare type of rock was first examined by Walter Harvey Weed and Louis V. Pirsson in 1895. The geologists coined the term and published the results of their studies the following year in Geology of the Little Rocky Mountains.

In addition to orthoclase and augite, shonkinite may contain a number of other minerals as well, including biotite, olivine, and nepheline. The rock does not, however, ever contain quartz and may only contain minor amounts of plagioclase feldspar. Shonkinite is closely related to several other relatively rare types of rock, such as theralite, essexite, and teschenite.

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