mineral
Blue agate slice
Microcrystalline quartz (chalcedony), SiO₂, commonly colored blue by dyes or inclusions
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent vivid blue interior with a darker gray-brown rind, waxy to vitreous luster, and cryptocrystalline structure. Agate lacks cleavage and has conchoidal fracture; specific gravity is about 2.6.
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Physical properties
Hardness 6.5–7 Mohs; translucent vivid blue interior with a darker gray-brown rind, waxy to vitreous luster, and cryptocrystalline structure. Agate lacks cleavage and has conchoidal fracture; specific gravity is about 2.6.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony in successive layers over long periods, typically during the Cenozoic or older volcanic episodes. The intense blue color in small polished slices is often enhanced by dyeing.
Uses & applications
Used as a decorative polished specimen, cabochon, paperweight, or jewelry component; natural blue agate is less common, while dyed material is inexpensive.
Geological facts
Agate is a banded variety of chalcedony, and its layers can preserve changing chemistry in the original cavity. The pictured piece appears cut and polished rather than naturally weathered.
Field identification & locations
Identify by its glassy/waxy surface, hardness, translucency, curved banding, and lack of cleavage; common sources include Brazil, Uruguay, Mexico, India, and Madagascar. A scratch test and inspection for dye concentration in cracks can help distinguish treated material.
