mineral
Agate Nodules
Cryptocrystalline Quartz (SiO2)
Mohs hardness 6.5-7, vitreous to waxy luster, conchoidal fracture, trigonal crystal system (microscopic), white streak, specific gravity 2.58-2.64. Shows translucent banding with red, brown, yellow, and white colors.
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Physical properties
Mohs hardness 6.5-7, vitreous to waxy luster, conchoidal fracture, trigonal crystal system (microscopic), white streak, specific gravity 2.58-2.64. Shows translucent banding with red, brown, yellow, and white colors.
Formation & geological history
Formed by silica-rich hydrothermal fluids depositing layer by layer inside cavities (gas bubbles/vesicles) within volcanic basalt or sedimentary rocks.
Uses & applications
Popular as lapidary material for polishing, cabochons, jewelry, decorative carvings, and mineral collection.
Geological facts
Agates are microcrystalline varieties of quartz, specifically chalcedony. The colorful banding comes from trace iron, manganese, and other mineral impurities present during formation layers.
Field identification & locations
Look for rounded, heavy nodules with pitted or weathered husks (cortex) that reveal translucent, colorful, banded quartz interiors when broken or cut open. Common in gravel deposits, riverbeds, and volcanic fields worldwide.
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