mineral
Carnelian agate (likely chalcedony)
Microcrystalline quartz, SiO₂; orange coloration commonly from iron oxides
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; translucent orange-red and cream banding, waxy to glassy luster, cryptocrystalline quartz, no visible cleavage, specific gravity about 2.6. The irregular polished-looking fragment may also contain druzy or calcite-like surface material, so exact identification from one image is limited.
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Physical properties
Hardness about 6.5–7 Mohs; translucent orange-red and cream banding, waxy to glassy luster, cryptocrystalline quartz, no visible cleavage, specific gravity about 2.6. The irregular polished-looking fragment may also contain druzy or calcite-like surface material, so exact identification from one image is limited.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing chalcedony and iron-bearing layers. Agate formation spans many geological ages, commonly in basaltic volcanic terrains.
Uses & applications
Used for beads, cabochons, carvings, ornamental objects, and collector specimens; historically used for seals and cameos. Common material is inexpensive, while vivid banded or well-polished pieces command more.
Geological facts
Carnelian is the orange-red variety of chalcedony; heat treatment can intensify its color. Agate’s bands record successive pulses of silica deposition.
Field identification & locations
Identify by its waxy luster, translucency, orange-red color, and lack of cleavage; it should resist scratching by a steel knife. Common localities include Brazil, Uruguay, India, Madagascar, and the western United States.
