Colour

Yellowish green, bright green or brownish green

Cause of  Colour

Uranium, Thorium and mainly radiation damage.

Optical Character

Low type metamicts may show a biaxial figure as they revert to a monoclinic structure or be almost amorphous, showing interference colours due to strain in crossed polars.

Pleochroism

None generally detected

Colour change

No

Spectrum; no polar, calibration in nm.

Diffuse and vague absorption bands at 660 and 520. Low type with anomalous spectrum (This may be a natural or heat treated metamict) – Three distinctive strong bands appear in the red instead of the usual single broad vague band. Other bands may be present.

Ordinary ray

Little or no change to spectrum.

Extraordinary ray

Little or no change to spectrum

Alpha ray

Not applicable

Beta ray

Not applicable

Gamma ray

Not applicable

Emission lines

No

Database reference

See Excel files on green gems

Notes

Many metamict zircons are from Sri Lanka. R.I. may be as low as 1.788 with little or no birefringence. Intermediate varieties, natural or heat treated, have a higher SG and RI as their crystalline structure is restored and may show an anomalous spectrum