How the red in Red Mountain came to be

Dear Science Mine: Why is Red Mountain belong primarily to the Mountain red? Greyson Formation, a dark-colored — A Butte resident mudstone that has largely been altered to slate. During the long time — Karen Porter is a senior Answer: Red Mountain is one of that the original sediments were research geologist for the the three peaks that form the skyline subjected to deep burial, lithified to Montana Bureau of Mines and of the Highland form rock, and finally uplifted to Geology, Butte, Montana, and Science Mountains form mountains, the rocks underwent may be reached via e-mail at Mine south of Butte. numerous chemical changes that [email protected]. These moun- formed new minerals in the rocks. tains are up- In the Greyson Formation, a — How does a GPS work? lifted blocks of large amount of iron sulfide accumu- Why is the sky blue? Need to very ancient lated to form such minerals as pyrite. know? You ask the questions and sedimentary When the iron sulfide minerals Montana Mind Expansion — a rocks (around 1 weather, the iron “rusts,” or oxi- group of Butte professionals and billion years dizes, turning the rock various lay people with expertise in all old) that were shades of red. fields of science and engineering once deposited Thus, Red Mountain is red — will provide the answer. Send as sand and because of the weathering of the KAREN PORTER your most perplexing query to mud in a large iron-sulfide minerals within its The Science Mind, care of The depression that occupied most of rocks. Montana Standard, Box 627, present-day western Montana. Many If you hike the trail leading up Butte 59703; or Colleen Elliott, thousands of feet of sediment accu- to the fire tower, you will have good geological engineering, Montana mulated in this depression — the opportunity to examine the Greyson Tech, [email protected]. This Belt Basin— and the rocks became Formation; although, it is not the column runs Saturdays in The what geologists call the Belt Super- only kind of rock present on the Standard. group. mountain. It is dark-colored where Within the Belt Supergroup, its broken surfaces are fresh, but many distinct formations have been stained red where it has been named. The rocks that make up Red weathered by air and water.