By: Marlene Affeld
Since biblical times agates have been considered power stones, talismans of protection and healing energy. The agates found in Montana are no exception. Native Americans believed the intriguing stone told stories from the earth mother and provided protection. It was the stone of warriors. Montana Moss Agate is considered by many to be the most powerful of all agates and is said to ward off storms.
Montana Moss Agate, a semi-precious stone found in the alluvial gravels of the Yellowstone River and its tributaries, is an exquisite and valued form of “chalcedony”, one of many types of the mineral, quartz. Montana Moss Agate is classified as a cryptocrystalline or microcrystalline quartz and has a hardness rating of 7.
Montana Moss Agate will take a high polish and is used in carvings and jewelry. The Montana Moss Agate is noted for the dendrite and ribbon effect in the rocks. Another type of Montana Moss Agate is sometimes called pepper rock for sprinkles of black found in it that resemble pepper grains.
Although agates of many different varieties are distributed around the world, this beautiful and unique agate is only found in eastern Montana. Most of these agates are located in gravel deposits from the Pleistocene age.
Over 80 million years ago, volcanic activity near what is now the town of Sidney, Montana created this incredible chalcedony known as Montana Moss Agate. Found along the entire length of the Yellowstone River, Montana Moss Agates are most plentiful within a 200 mile stretch between Custer and Sidney, Montana.
Centered in what is now the Yellowstone Park area of Montana and Wyoming, this massive volcanic activity stretched from the Rocky Mountain front in south-central Wyoming north across eastern Montana and extended into Saskatchewan and Manitoba, Canada.
During the Pleistocene age, Eastern Montana was a shallow inland ocean surrounded by a majestic forest of mighty sequoias and redwoods. As volcanoes spewed forth molten lava and ash, millions of acres of forests were entombed. This process went on for thousands of years with trees growing to maturity and then decimated by mega tons of lava. As the lava cooled, most of the trees were consumed by the heat, however; some parts of trunks and branches were trapped in the cooling lava. When the rains came, mineral laden silica water flowed into the cracks and pockets left by the molten lava and the dying trees. As rainfall after rainfall filled these cavities with liquid silica, Montana Moss Agate was formed.
Montana Moss Agate is normally a soft creamy yellow to almost clear with embedded intrusions or “moss structures” in variegated shades of tawny red to blackish brown. These bands or inclusions often appear to be trees or mountain ranges and are crafted into prized jewelry pieces, each as unique as snowflakes.
Examples of macro-crystalline forms of quartz include rose quartz, smoky quartz, amethyst, aemtrine and citrine. Agates and chalcedony in other forms such as carnelian and jasper are microcrystalline or cryptocrystalline forms of quartz.
Agate hunting is a popular pastime for young and old alike. In early spring agate hunters will often take boats down the Yellowstone River, stopping at gravel and sandbars to hunt for the elusive mineral.
In 1969, Montana Moss Agate, along with the Yogo Sapphire, were designated Montana’s State gemstones.