Montana State Gemstone

Agate

(SiO₂ - Silicon Dioxide)

Adopted in 1969.

Montana sapphires and Montana agates have shared honors as the state's gemstones since 1969. Recognition was a long time in coming. Montana's Council of Rock and Mineral Clubs supported not only the sapphire for gemstone honors, but advocated equal recognition for the exquisite and ever-varying Montana agate, found in abundance along the Yellowstone River to the east. Agates are found in southern and eastern Montana.

The Montana agate is usually a creamy light yellow to almost clear color with embedded moss structures in varying shades of brownish red to black. Most of these Montana agates are found in gravel deposits from the Pleistocene age (10,000 - 1,6000,000) in the area of the Yellowstone River and its tributaries.

Agate is one of the most varied and desired forms of "chalcedony" which is one of the many varieties of quartz. Scientifically classified as a cryptocystalline or microcrystalline quartz, it has a hardness of between 6.5-8 on the Mohs scale. They take an exceptional polish and are used extensively in jewelry and carvings. They're polished, not cut, to make gemstones and jewelry.

Agates in general come in many different forms and the main conditions necessary for agate formation, are the presence of silica from devitrified volcanic ash, water from rainfall or ground sources, and manganese, iron and other mineral oxides that form the bands and inclusions.

Montana Moss Agate ia a name given to the beautiful chalcedony found, most abundantly, in the alluvial gravels of the Yellowstone River, would probably be better named Yellowstone Agate, because it's genesis was centered in the Yellowstone Park area.

Eastern Montana was mostly a shallow inland ocean, almost a swamp with huge forests lining it's shores and islands of volcanoes spewing forth lava to entomb parts of the forest in lava and ash . The bowels of Yellowstone bulged and roared and flowed mountains of lava that decimated thousands of acres of mighty redwoods and sequoias for hundreds of miles around. This decimation continued for hundreds of years with layer upon layer of forests growing up and then being driven down under the ponderous weight of all the mega-tons of lava and ash. The hot lava devoured most of the wood in it's rush to cover the trees, but some of the shape and ingredients of the limbs remained trapped in the cooling lava. When the time of volcanoes and lava was subdued and the rains came, mineral laden silica-water flowed into the cavities and pockets left by the dying trees and bubbling lava. As flow after flow slowly filled the pockets with liquefied silica, Montana Agate was born.

Between the sapphire and the agate, Montana's east and west, heritage and hobbies, are represented.

Agate is the Mystical birthstone for the month of September and the birth stone for the Zodiac sign of Gemini.

Folklore: Balances emotions, discerns the truth, accepts circumstances, powerful emotional healer.
 

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