sedimentary
Agate Nodule / Chalcedony
Silicon Dioxide (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, grayish-white to translucent color, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, grayish-white to translucent color, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65
Formation & geological history
Formed through the deposition of silica from groundwater solutions in the cavities (vesicles) of volcanic or sedimentary rocks, often developing in concentric layers over millions of years.
Uses & applications
Commonly used in lapidary arts, decorative items, tumbled stones, and collector specimens.
Geological facts
Agate is a variety of chalcedony. The pitted, bumpy surface seen on this weathered specimen is often referred to as 'sugar' texture or weathered rind resulting from exposure to acidic soils.
Field identification & locations
Can be identified by its conchoidal fracture, waxy luster, hardness capable of scratching glass, and microcrystalline structure. Frequently found in river gravels, glacial drift, and volcanic regions worldwide.
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