Topaz, Peridot, Zircon, Kyanite
Color: Colorless, white, pale blue, light green, yellow, brownish-yellow, or red
Luster: Vitreous
Hardness: 8
Specific Gravity: 3.4 – 3.6
Crystal System: Orthorhombic
Name: Named after the island of Topazios (now called Zabargad or Saint John’s Island) in the Red Sea. In antiquity, the name was probably used for the gemstone now known as peridot.
Formula:
Color: Colorless, white, pale blue, light green, yellow, brownish-yellow, or red
Luster: Vitreous
Hardness: 8 (Mohs)
Specific Gravity: 3.4 – 3.6
Crystal System: Orthorhombic (Note: Topaz may be orthorhombic or triclinic depending on the F:OH ratio.)
Name Origin: Named after the island of Topazios (currently known as Zabargad or St. John’s Island) in the Red Sea. In antiquity, the name likely referred to the gemstone now known as peridot.
Occurrence: Found in pegmatites and high-temperature quartz veins, as well as in cavities within granites and rhyolites.
Geological Context: In natural topaz, approximately 30% of the F (fluorine) sites are occupied by OH (hydroxyl). In very rare instances, OH-dominant members have been described in high-pressure rocks; see “Unnamed (OH-analogue of Topaz)” (Zhang et al., 2002). A pure synthetic OH-analogue of topaz has been synthesized under high-pressure (55–100 kbar) and high-temperature (up to 1000°C) conditions (Wunder et al., 1993).
