Agate
Banded chalcedony, laid down layer by layer inside cavities in lava.
- Family
- Chalcedony
- Formula
- SiO₂
- Mohs
- 6.5 to 7
- System
- Trigonal
Drag to turn
Science
Agate forms when silica-rich water seeps into gas bubbles in cooling lava and deposits chalcedony on the walls in successive bands. Each band records a change in water chemistry. Hundreds of named varieties exist, defined by pattern and place: lace, fortification, moss, dendritic, fire.
- Mineral
- Chalcedony (variety)
- Formula
- SiO₂
- Crystal system
- Trigonal
- Mohs hardness
- 6.5 to 7
- Specific gravity
- 2.58 to 2.64
- Refractive index
- 1.530 to 1.540
- Lustre
- Waxy to vitreous
- Colours
- Banded, Grey, Brown, Blue, Red
Composition
SiO₂. Made of Silicon, Oxygen, with trace Iron, Manganese responsible for colour.
Origin
- BrazilRio Grande do Sul
- Uruguay
- India
- Mexico
- GermanyIdar-Oberstein, cutting centre
- United StatesLake Superior, Oregon
Filled dots are primary sources
Rarity
Abundant. Most bright agate slices are dyed; natural fine banding in strong colour is less common.
- 1 Abundant
- 2 Common
- 3 Uncommon
- 4 Rare
- 5 Exceptional
Hardness
Agate sits at 6.5 to 7 on the Mohs scale. It will scratch glass and holds a polish in daily wear.
Energy
Associations from crystal-healing tradition, recorded here as folklore. They are not medical claims.
Chakras
- Root
Element
- Earth
Zodiac
- Gemini
- Virgo
Planets
- Mercury
Properties
- Stability
- Patience
- Balance
- Endurance
Lore
Theophrastus named it around 300 BCE after the Achates river in Sicily. Babylonians, Egyptians and Romans all cut it for seals, bowls and eye beads.
Idar-Oberstein in Germany built an entire industry on cutting agate from the 1400s, then on Brazilian rough after local mines ran out, which is how the dyeing techniques were perfected.
- DyeChalcedony is porous; blue, pink and green slices are almost always dyed.
- Thunder eggsAgate-filled nodules from rhyolite, Oregon's state rock.