Zoisite Visible Spectra (400 - 1000 nm)
The blue variety, tanzanite, is colored by vanadium. It is highly pleochroic before it is heat-treated for the commercial gem market. Pink zoisite contains Mn3+. Green varieties contain Fe3+.
Images of the zoisite absorption spectrum
spectrum, from Tanzania,
normalized to 3.0 mm thick. The color of this crystal varies
with the direction in which it is observed. It varies from greenish
to deep blue to red-violet. Data Files: E||a=gamma;
- GRR 2292 spectrum
- blue zone, from Arusha Region, Tanzania, normalized to 3.0 mm thick.
This crystal consists of two zones, one yellow and the other blue. In
polarized light, each of these zones shows distinct pleochroism. Data
Files: E||a=gamma; E||b=alpha; E||c=beta.
- GRR 2292 spectrum - yellow zone from Arusha Region, Tanzania, normalized to 3.0 mm thick. E||a=gamma; E||b=alpha; E||c=beta.
- GRR 2891 spectrum,
from the Merelani Hills, Tanzania, normalized to 5.0 mm thick. This
sample was collected on the surface and was exposed to the sun for an
unknown period of time. The material is bluish and lacks the brown color of most tanzanite when it is mined underground. Yet, it still shows spectacular pleochroism in linerally polarized light. Data Files: E||a=gamma;
data from Faye and Nickel (1971) showing the spectrum of a
tan colored zoisite (Tanzanite) before and after heating to
Pale Yellow Zoisite
Faye GH and Nickel
EH (1971) On the pleochroism of vanadium-bearing zoisite from Tanzania.
Canadian Mineralogist p812.
Langer K, Tillmanns E, Kersten M, Almen H, Arni RK (2002) The crystal chemistry of Mn3+ in the clino- and orthozoisite structure types, Ca2M33+[OH|O|SiO4|Si2O7]:
A structural and spectroscopic study of some natural piemontites and
“thulites” and their synthetic equivalents. Z Kristallogr 217:563-580
last updated: 20-Dec-2014