Moh’s hardness: 8.5
Refractive index: 1.744-1.755
Critical angle: 35°
Specific gravity: 3.7-3.72
Fracture: Weak, conchoidal
Dispersion: Medium (.015)
Heat sensitivity: Low,
but cracks and cleavages may open up and travel with heat.
– very weak (reddish to yellowish or yellow to pale-green).
refraction): Medium (.011)
Crystal structure: Orthorhombic
Treatments: May be irradiated.
with 8,000 grit helps polishing go much faster.
Polishing: Ceramic or
zinc lap with 50,000 or 100,000 diamond. Tin/lead or tin with
alumina creates a good polish, but is slow.
Comments: True color
changing stones exhibit a strong change in color when the light source
switches from daylight or fluorescent to incandescent. Many stones
exhibit a shift in color, but true color change stones must exhibit
a dramatic change, such as green to red or blue to red. In order
for a chrysoberyl to be considered an alexandrite, a strong color change
must be present. True alexandrite is extremely rare and expensive.
Beware that very good synthetic alexandrite is currently on the market.
Corundums, spinels and garnets may also display color change.