sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, translucent to opaque appearance, conchoidal fracture, and specific gravity of 2.58-2.64.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, translucent to opaque appearance, conchoidal fracture, and specific gravity of 2.58-2.64.
Formation & geological history
Formed by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks, often developing in concentric bands over millions of years.
Uses & applications
Used extensively in making ornamental items, jewelry, carvings, laboratory mortars and pestles, and as a popular specimen for rock collectors.
Geological facts
Agate is a variety of chalcedony and is often associated with volcanic rocks. Montana, near the geographic coordinates provided, is notably famous for producing the Montana Agate, which often features distinctive reddish-brown dendritic inclusions caused by iron or manganese oxides.
Field identification & locations
Easily identified by its waxy luster, conchoidal fracture, and characteristic banding or translucent layers. Frequently found in river gravels and volcanic regions.
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