gemstone
Montana Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness: 6.5-7 on the Mohs scale, Color: Translucent with yellow, brown, and grey inclusions, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline quartz), Cleavage: None, Specific Gravity: 2.60-2.65
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 on the Mohs scale, Color: Translucent with yellow, brown, and grey inclusions, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline quartz), Cleavage: None, Specific Gravity: 2.60-2.65
Formation & geological history
Formed in Cenozoic volcanic rocks where silica-rich solutions filled gas cavities in basalt, often stained by iron and manganese oxides over millions of years.
Uses & applications
Used primarily in lapidary arts, gemstone jewelry, and as a popular collectible specimen.
Geological facts
Montana agates are famous for their characteristic dendritic inclusions caused by trapped iron and manganese oxide branches that resemble miniature trees or moss.
Field identification & locations
Identified by its waxy luster, conchoidal fracture, and distinct brownish-yellow and greyish banding. Commonly found in alluvial gravels along the Yellowstone River and surrounding areas in Montana.
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