Montana Agate

Montana Agate

Agate is a moderately hard rock, primarily composed of silica (quartz). Montana agate and sapphire are the two State gemstones of the State of Montana. Montana agate is sometimes also referred to as “moss agate” (agate that has colored inclusions that may resemble moss) or “scenic agate”.

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. In general, agates form when silica in groundwater is deposited in openings in the subsurface.

It is generally believed that Montana agates were formed as the result of volcanic activity in the Yellowstone Park area millions of years ago, which deposited a tremendous amount of silica-rich ash over a wide area. Some Montana agates, such as “limb casts”, appear to have originated from wood that became buried by ash and fossilized after the volcanic activity.

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

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