mineral
Alexandrite (or Quartz with Chrysoberyl/Phenakite crystal form / Feldspar inclusions)
Chrysoberyl (BeAl2O4) or Quartz (SiO2)
Hardness: 8.5 (if Chrysoberyl/Alexandrite) or 7 (if Quartz). Color: Greyish-purple to bluish/smoky with reddish-pink clay or hematite coating on outer crystal faces. Luster: Vitreous to sub-adamantine. Crystal structure: Orthorhombic hexagonal-like cyclic twin habit or hexagonal prismatic quartz face.
- Hardness
- 8
- Luster
- Vitreous to sub-adamantine
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Physical properties
Hardness: 8.5 (if Chrysoberyl/Alexandrite) or 7 (if Quartz). Color: Greyish-purple to bluish/smoky with reddish-pink clay or hematite coating on outer crystal faces. Luster: Vitreous to sub-adamantine. Crystal structure: Orthorhombic hexagonal-like cyclic twin habit or hexagonal prismatic quartz face.
Formation & geological history
Formed in granitic pegmatites and mica schists undergoing regional metamorphism. The location in Minas Gerais, Brazil (20.1°S, 42.0°W) is world-famous for pegmatitic gems including alexandrite, chrysoberyl, emerald, and smoky quartz.
Uses & applications
Extremely valuable as a gemstone when gem-grade; highly sought after by mineral collectors for uncut crystal habits.
Geological facts
Minas Gerais is one of the most famous pegmatite districts in the world. Cyclic twinned alexandrite crystals from this region often display classic six-sided pseudo-hexagonal prismatic shapes with distinct reddish-brown matrix coating.
Field identification & locations
Identify by testing hardness (scratches quartz easily if alexandrite/chrysoberyl), checking color change under incandescent vs fluorescent light, and examining hexagonal or cyclic twin face geometry.
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Schist
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Potassium Feldspar (Orthoclase)
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