“Northosite / Anorthosite is a phaneritic, (an igneous rock whose microstructure is made up of crystals large enough to be distinguished with the unaided eye), intrusive igneous rock characterized by a predominance of plagioclase feldspar (90–100%), and a minimal mafic (a silicate mineral or igneous rock that is rich in magnesium and iron) component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.
Anorthosite on Earth can be divided into two types: Proterozoic anorthosite (also known as massif or massif-type anorthosite) and Archean anorthosite. These two types of anorthosite have different modes of occurrence, appear to be restricted to different periods in Earth’s history, and are thought to have had different origins.
Lunar anorthosites constitute the light-coloured areas of the Moon’s surface and have been the subject of much research.”
Montana gets the nickname “Big sky country” because of views like this one - mountains in the distance over Butte Montana (Mountains probably part of the Idaho Batholith, an igneous intrusion that contributed to why there are mining towns like Butte in this area in the first place).