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Montana Agate

Pretty semi precious gemstone Montana Agate comes from Montana.

It comes from near the Yellowstone River.

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. Montana Moss Agate is found throughout the 670 mile length of the river.

The agate originally was formed in the Yellowstone National Park area of Wyoming as a result of volcanic activity approximately 65 million years ago.

In Montana Agate cabochons the red color is the result of iron oxide, the black and brown is the result of manganese oxide and the red and orange came from iron oxide. On very rare occasions you can get a green from copper. 

It is considered a moss agate because of the mossy shape of its inclusions, but more often it is banded, polka dotted or has dendrites.

Most of the Montana Agate rough is broken up and found in smaller pieces.  Chunks larger than 10 pounds are rare.  However the largest piece ever found weighed 63.5 pounds! 

Montana Agate generally has a coating or skin.

Agate is a microcrystalline Quartz and has a hardness of 7, which makes the Montana Agate designer cabochons very wearable.

Montana Agate has been the state of Montana's official state gemstone (along with Montana Sapphire) since 1969.

  • Montana Moss Agate Matched Pairs Triangle Stone Cabochons #2 Montana Moss Agate Matched Pairs Triangle Stone Cabochons #2

    Montana Agate Matched Pair Cabochons #2

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 27 mm by 11.5 mm and 4 mm thick. These weigh about 6.5 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $48.00
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  • Montana Agate Matched Pair Cabochons Loose Stones #19 Montana Agate Matched Pair Cabochons Loose Stones #19

    Montana Agate Matched Pair Cabochons #19

    Oval shaped matched pair milky translucent with black spots semi precious gemstone Montana Agate designer cabochons 26 mm by 12.50 to 20 mm and 4 mm thick. These weigh about 15 carats each. Pretty semi precious gemstone Montana Agate comes...

    $56.00
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  • Montana Agate Large Matched Pairs Designer Cabochons Stones #15 Montana Agate Large Matched Pairs Designer Cabochons Stones #15

    Montana Agate Matched Pair Cabochons #15

    Larger oval shaped matched pair milky translucent with black spots semi precious gemstone Montana Agate designer cabochons 41 mm by 14 mm and 4 mm thick. These weigh about 15.5 carats each. Pretty semi precious gemstone Montana Agate comes...

    $100.00
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  • Montana Agate Matched Pair Cabochons Semiprecious Stones #5 Montana Agate Matched Pair Cabochons Semiprecious Stones #5

    Montana Agate Matched Pair Cabochons #5

    Oval shaped matched pair milky translucent with black spots semi precious gemstone Montana Agate designer cabochons 23.5 mm by 7.50 to 13 mm and 3.5 mm thick. These weigh about 7.5 carats each. Pretty semi precious gemstone Montana Agate...

    $36.00
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  • Montana Agate Matched Pair Cabochons Semiprecious Stones  #13 Montana Agate Matched Pair Cabochons Semiprecious Stones  #13

    Montana Agate Matched Pair Cabochons #13

    Oval shaped matched pair milky translucent with black spots semi precious gemstone Montana Agate designer cabochons 22 mm by 7.50 to 14.5 mm and 4 mm thick. These weigh about 8.5 carats each. Pretty semi precious gemstone Montana Agate comes...

    $36.00
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  • Montana Agate Translucent Cabochon Loose Stone #20 Montana Agate Translucent Cabochon Loose Stone #20

    Montana Agate Cabochon #20

    Oval shaped translucent with black and brown inclusions semi-precious gemstone Montana Agate designer cabochon 39 mm by 23 mm and 6 mm thick. Pretty semi-precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana...

    $36.00
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  • Montana Agate Designer Cabochon Loose Stone for Jewelry Making #19 Montana Agate Designer Cabochon Loose Stone for Jewelry Making #19

    Montana Agate Cabochon #19

    Oval shaped gray translucent with black and brown polka dots semi precious gemstone Montana Agate designer cabochon 43 mm by 26 mm by 5 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In...

    $40.00
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  • Montana Agate Triangles Pairs Cabochon Stones Jewelry Making #23 Montana Agate Triangles Pairs Cabochon Stones Jewelry Making #23

    Montana Agate Matched Pair Cabochons #23

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 33 mm by 13 mm and 3 mm thick. These weigh about 7 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $48.00
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  • Montana Agate Matched Pairs Cabochon Stones Jewelry Making #3 Montana Agate Matched Pairs Cabochon Stones Jewelry Making #3

    Montana Agate Matched Pair Cabochons #3

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 32 mm by 10 mm and 3.5 mm thick. These weigh about 6 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $48.00
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  • Montana Agate Matched Pairs Translucent Loose Cabochon Stones #12 Montana Agate Matched Pairs Translucent Loose Cabochon Stones #12

    Montana Agate Matched Pair Cabochons #12

    Oval shaped matched pair milky translucent with black and brown semi precious gemstone Montana Agate designer cabochons 18.5 mm by 9 mm and 4 mm thick. These weigh about 4.5 carats each. Pretty semi precious gemstone Montana Agate comes from near...

    $24.00
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  • Montana Agate Matched Pairs Translucent Dots Cabochon Stones #9 Montana Agate Matched Pairs Translucent Dots Cabochon Stones #9

    Montana Agate Matched Pair Cabochons #9

    Triangle shaped matched pair milky translucent with black and brown semi precious gemstone Montana Agate designer cabochons 31.5 mm by 9 mm and 3.5 mm thick. These weigh about 5.5 carats each. Pretty semi precious gemstone Montana Agate comes from...

    $40.00
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  • Montana Agate Matched Pairs Translucent Cabochon Stones #20 Montana Agate Matched Pairs Translucent Cabochon Stones #20

    Montana Agate Matched Pair Cabochons #20

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 29 mm by 9 mm and 3 mm thick. These weigh about 4.5 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $40.00
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  • Montana Moss Agate Matched Pairs Triangle Stone Cabochons #21 Montana Moss Agate Matched Pairs Triangle Stone Cabochons #21

    Montana Agate Matched Pair Cabochons #21

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 26 mm by 8 mm and 3 mm thick. These weigh about 3.5 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $36.00
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  • Montana Moss Agate Matched Pair Triangle Designer Cabochons #17 Montana Moss Agate Matched Pair Triangle Designer Cabochons #17

    Montana Agate Matched Pair Cabochons #17

    Triangle shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 25 mm by 10 mm and 3 mm thick. These weigh about 4.5 carats each. Pretty semi precious gemstone Montana Agate comes from near the...

    $36.00
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  • Montana Moss Agate Translucent Semiprecious Stone Oval Cabochon #10 Montana Moss Agate Translucent Semiprecious Stone Oval Cabochon #10

    Montana Agate Cabochon #10

    Milky but very translucent with black and brown oval shaped Montana Agate designer cabochon 29 mm by 22 mm and 4.5 mm thick.  Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana Agate...

    $24.00
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  • Montana Agate Loose Stone Cabochon Jewelry Making Supplies #1 Montana Agate Loose Stone Cabochon Jewelry Making Supplies #1

    Montana Agate Cabochon #1

    Oval shaped milky translucent with black and brown banding semi precious gemstone Montana Agate designer cabochon 33.5 mm by 14 mm and 5 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In...

    $30.00
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  • Montana Agate Translucent Semiprecious Stone Oval Cabochon #11 Montana Agate Translucent Semiprecious Stone Oval Cabochon #11

    Montana Agate Cabochon #11

    Milky but very translucent with black and brown oval shaped Montana Agate designer cabochon 30 mm by 18 mm and 4 mm thick.  Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana Agate...

    $24.00
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  • Montana Agate Translucent Long Triangle Cabochon Stone #21 Montana Agate Translucent Long Triangle Cabochon Stone #21

    Montana Agate Cabochon #21

    Long triangle shaped milky translucent with black spots semiprecious gemstone Montana Agate designer cabochon 46 mm by 9 mm and 3 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana...

    $20.00
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  • Montana Agate Translucent Small Cabochon Jewelry Stone #5 Montana Agate Translucent Small Cabochon Jewelry Stone #5

    Montana Agate Cabochon #5

    Tiny trapezoid shaped milky translucent with black spots semiprecious gemstone Montana Agate designer cabochon 18 mm by 4 to 7 mm and 3.5 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana...

    $8.00
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  • Montana Agate Translucent Small Triangle Cabochon Jewelry Stone #18 Montana Agate Translucent Small Triangle Cabochon Jewelry Stone #18

    Montana Agate Cabochon #18

    Tiny triangle shaped milky translucent with black spots semiprecious gemstone Montana Agate designer cabochon 19 mm by 5 mm and 3 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana...

    $8.00
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  • Montana Moss Agate Translucent Small Triangle Cabochon Stone #15 Montana Moss Agate Translucent Small Triangle Cabochon Stone #15

    Montana Agate Cabochon #15

    Tiny triangle shaped milky translucent with black spots semiprecious gemstone Montana Agate designer cabochon 16 mm by 9 mm and 3 mm thick. Pretty semi precious gemstone Montana Agate comes from near the Yellowstone River in Montana. In Montana...

    $8.00
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  • Montana Agate Small Moss Matched Pair Cabochons Designer #14 Montana Agate Small Moss Matched Pair Cabochons Designer #14

    Montana Agate Matched Pair Cabochons #14

    Short trapezoid shaped matched pair milky translucent with black semi precious gemstone Montana Agate designer cabochons 7 mm by 3 to 9 mm wide and 3.5 mm thick. These weigh about 4.5 carats each. Pretty semi precious gemstone Montana Agate...

    $20.00
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  • Montana Agate Matched Pairs Polka Dotted Cabochons Stones #18 Montana Agate Matched Pairs Polka Dotted Cabochons Stones #18

    Montana Agate Matched Pair Cabochons #18

    Triangle shaped matched pair milky translucent with black and brown spots semi precious gemstone Montana Agate designer cabochons 24 mm by 9 mm and 4 mm thick. These weigh about 6.5 carats each. Pretty semi precious gemstone Montana Agate...

    $36.00
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  • Montana Agate Matched Pairs Transparent Cabochons Stones #8 Montana Agate Matched Pairs Transparent Cabochons Stones #8

    Montana Agate Matched Pair Cabochons #8

    Triangle shaped matched pair milky translucent with black and brown spots semi precious gemstone Montana Agate designer cabochons 29 mm by 11 mm and 4 mm thick. These weigh about 6.5 carats each. Pretty semi precious gemstone Montana Agate...

    $40.00
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