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Montana Moss Agate

Montana Moss with 3 planes of small dendrites

Colliding Galaxies

Montana Moss Agate with Dendrites in the shape of a ship

Clipper ship

World Class Gallery You have entered the Montana Moss Agate gallery.  The Montana Moss Agates are each one of a kind.  Iron oxides tint the agates to red and manganese spread into layers making the famous black dendrite tree and flower patterns.   Internal boytroidal patterns often show as bubbly cloud like formations on highly polished specimens. Large agates take long time to grind smooth.   Many of the larger agates take 2 to 3 months on rough grind alone.  The exceptional glass mirror finish is obtained by running a full month on 400 grit and polish.   The Montana Moss Agates formed over 65 million years ago as volcanoes began erupting  along the eastern front of what is now the Rocky Mountains.  For millions of years massive lava flows buried the land including entire forests.  Sometimes wood remained and was mineralized to become petrified wood and sometimes only the impression of the wood remained and became what is called a limb cast.  Most agates from around the world including the Montana Moss Agates were formed within cavities and gas pockets within the lava.  Most of these cavities were caused by trapped steam and gasses trying to escape through the lava as the lava cooled.  Mineral water with silica (SiO2) flowed in and out of these cavities leaving behind layer after layer of agate.   The central Montana mountains were formed between 40 and 50 million years ago.  The lifting and shifting movement of the continental plate caused the break up of the original lava beds containing the agate nodules, limb casts and petrified wood.  For tens of millions of years the harder agates eroded out of the softer basalt.  During the last 2 million years glaciers and rivers carried the agates east along a wide basin, where the Yellowstone River now flows.  I'm sure the river was named for the agates.  The French trappers called it River of the Yellow Stone.  Standing on the shore of the Yellowstone looking toward the sun at sunrise or sunset you will see agates glowing bright yellow everywhere you look.    Please enjoy.

Hollow Limb Cast

Hollow Limb cast with dendrites

Montana Moss Agate Rare Blue

This is one of the vary rare blue Montana agates. The skin was greenish / gray before tumbling. Nothing to indicate blue.

Montana Moss Agate with many flower dendrites

These dendrites were under a layer of quartz. The dendrites were exposed by tumbling away the softer quartz layer.

Montana Moss Agate with banding lines

Montana Agates rarely show this tight of banding the red in iron oxides.

Montana Moss Agate with fortification type banding lines

Montana Agates rarely show this kind of banding. I think this one was a broken slice of a limb cast.

Montana Moss Agate with the form of an animal

The black dendrites often show pictures. Less common is a picture in the red iron oxide area.

Montana Moss Agate with parallel bands

Unusual banding of different colors and small dendrites.

Montana Moss Agate with unusual pattern.

The pattern in this agate might have been formed by a bark limb cast.
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