Montana is known as The Treasure State, and it is very fitting when it comes to rocks and minerals.
Montana Agate is probably the most well known rock from Montana! Montana Agate comes from near the Yellowstone River in Montana. Montana Agate is one of the alluvial agates, it is not found in-site, but in the Flaxville gravel deposits scattered over a huge area encompassing thousands of square miles. The agate originally was formed in the Yellowstone National Park area of Wyoming as a result of volcanic activity. In Montana Agate the red color is the result of iron oxide, the black is the result of manganese oxide. It is considered a moss agate. Montana Agate has been the state of Montana's official state gemstone (along with Montana Sapphire) since 1969.
The second most well known rock from Montana is the Montana Sapphire. Sapphire is a variety of corundum. In 1865, the first sapphires found in the U.S. were found in the gravels of the Missouri River in Lewis and Clark County, Montana. Later it was also found in Dry Cottonwood Creek in Deer Lodge County in 1889, on Rock Creek in Granite County in 1892, and in Yogo Gulch in Judith Basin County in 1895. Small amounts of sapphire also are recovered from Quartz Gulch in Granite County, Pole Creek in Madison County, the Missouri River in Chouteau County, and Brown's Gulch in Silver Bow County. In addition star sapphires have are found in Beaverhead and Madison Counties. Montana sapphires can be found in the Royal Crown Jewels of England. Sapphires, which were thrown away by miners in the gold rush days, are now the most valuable gemstones found in America.
Montana is also very well known for its Native Copper deposits, was included in the gold rush days when gold was discovered in 1864, and has produce lots of silver, zinc manganese and coal. Bannack, Virginia City, and Marysville were predominantly gold; Philipsburg was predominantly silver and manganese; and Butte was predominantly copper. Butte began as a mining town in the 19th century in the Silver Bow Creek Valley, located high in the Rockies straddling the Continental Divide. Originally only gold and silver were mined in the area, but the advent of electricity caused a soaring demand for copper, which was abundant in the area. Known as “The Richest Hill in the World”, over a billion tons of copper ore, silver, gold, and other metals were extracted from the rock of southwestern Montana, making the mining town of Butte one of the richest communities in the country.
My personal favorite Montana rock is the lovely Covellite. Covellite is a rare mineral composed of copper sulfide. It is a pretty metallic purplish blue with golden pyrite inclusions. This material came from the Leonard Mine in Butte, Montana.
Today the state is world-renown for its dinosaur fossil sites too. Montana designated the duck-billed dinosaur Maiasaura peeblesorum as its official state fossil in 1985. Maiasaura peeblesorum lived on the coastal plains and lowlands about 70 million years ago. Fossil localities have yielded multiple nests and the remains of over 10,000 individuals. One of the most significant paleontological discoveries came in 1978, when fossils of a nesting colony of duck-billed dinosaurs were found west of Choteau, Montana, now known as ‘Egg Mountain’.
There are lots of great rockhounding spots and pay for diggings sites in Montana. Crystal Park features public diggings for smokey quartz, amethyst and clear quartz crystals. You can also find plenty of crystals and unique rocks along the ridge lines and slopes around Branham Lakes. Both Virginia City and Nevada city as well as Alder provide "pay for sites" for gold and garnet (but if you know what you are doing you can find garnet about everywhere.) Sheridan Montana is located in the heart of the Ruby Valley, It is surrounded by 7 different mountain ranges. Mining was the main reason for its existence so there are a ton of areas you can go dig around in, especially in the mine tailings.
See my page on Rockhounding Rules for general information on the rules of collecting rocks on various lands.
Here at OakRocks we carry a variety of Montana rocks, including Montana Agate and gorgeous Covellite cabochons.