Chalcedony
Variety SiO2
Also called Calcedony
About it
Quartz made of microscopic fibres, so it has a waxy lustre and is translucent rather than clear. The umbrella name for agate, carnelian, chrysoprase, and onyx; plain grey-blue chalcedony fills cavities in lavas worldwide.
- 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
- white, grey, blue, lavender, yellow, brown
- Transparency
- translucent
- Cleavage and fracture
- none; conchoidal to uneven fracture
- Under UV light
- some glows green under shortwave UV
Typical values: real specimens vary. For more, see mindat.org.