Agate
Variety SiO2
About it
Chalcedony laid down in concentric bands inside gas holes in lava or nodules in other rocks. Brazil, Uruguay, Mexico, Botswana, and the Lake Superior region are famous sources.
- Type
- Variety
- Group
- Quartz variety (chalcedony)
- Formula
- SiO2
- Hardness (Mohs)
- 6.5–7
- Specific gravity
- 2.57–2.64
- Streak
- white
- Lustre
- waxy, vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- every colour, in bands
- Transparency
- translucent, opaque
- Cleavage and fracture
- none; conchoidal to uneven fracture
- Under UV light
- some bands glow green under shortwave UV
Typical values: real specimens vary. For more, see mindat.org.