mineral
Agate / Chalcedony Pebble
Silicon Dioxide (SiO2)
Hardness of 6.5-7 on Mohs scale; waxy to vitreous luster; microcrystalline/cryptocrystalline quartz structure; color ranges from grayish-tan, beige, to brownish tones; translucent when backlit.
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Physical properties
Hardness of 6.5-7 on Mohs scale; waxy to vitreous luster; microcrystalline/cryptocrystalline quartz structure; color ranges from grayish-tan, beige, to brownish tones; translucent when backlit.
Formation & geological history
Formed by low-temperature deposition of silica from groundwater within cavities of volcanic or sedimentary rocks, often weathered out into stream beds and river gravels.
Uses & applications
Popular for lapidary arts, rock tumbling, cabochon cutting, ornamental decor, and casual rockhounding collections.
Geological facts
Agates and chalcedony are composed of microscopic, intergrown crystals of quartz and moganite. Water-worn river pebbles like this often exhibit pitted 'orange peel' surface textures.
Field identification & locations
Look for translucency around thin edges when held up to light, smooth water-worn surfaces, and a scratch test indicating high hardness (will scratch glass). Commonly found in gravel bars, dry creek beds, and glaciated regions.
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