Sard
Variety SiO2
About it
Darker brown-red chalcedony that grades into carnelian with no sharp line between them. Used since ancient times for seals and carved intaglios.
- 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
- brownish red, dark brown
- Transparency
- translucent, opaque
- Cleavage and fracture
- none; conchoidal to uneven fracture
Typical values: real specimens vary. For more, see mindat.org.