Agate
Agate is banded chalcedony — microcrystalline quartz that forms in concentric layers inside volcanic vesicles (gas bubbles) or other cavities. The banding results from periodic changes in silica-rich groundwater chemistry. Lake Superior agates are among the most prized in the world, known for their deep red and orange iron-stained bands.
Physical Properties
Chemical Formula
SiO₂ (banded chalcedony)
Hardness (Mohs)
6.5–7
Color
Any color, typically banded in multiple colors
Luster
Waxy to vitreous
Crystal System
Hexagonal (microcrystalline)
Streak
White
Cleavage
None
Specific Gravity
2.6
🔍 Field Identification Tips
Look for waxy luster, concentric banding when sliced, and translucency when held to light. Unlike regular quartz, agate is microcrystalline so you won't see individual crystals. Heavier than glass.
Varieties & Forms
📍 Where to Find Agate in the US
Uses & Applications
Jewelry, cabochons, decorative objects, bookends, slabs. One of the most popular collecting targets.
💰 Collector Value Guide
Raw Lake Superior agates: $5–$100+. Polished slabs: $20–$500. Fire agate cabochons: $50–$500. Oregon thunder eggs: $10–$200.
Find Agate With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.