Colour

Yellowish green to brownish green

Cause of colour

Ferrous iron

Optical Character

Biaxial positive

Pleochroism

very weak – two shades of green

Colour change

No

Spectrum; no polar Calibration in nm.

Three evenly spaced weak narrow bands at 453; 573 and 493; Darker stones may show a weak diffuse bands at 529 and 635. 

Ordinary ray

Not applicable

Extraordinary ray

Not applicable

Alpha ray

493 extends to 495 and other two main bands are very weak

Beta ray

Three main bands are present but weak

Gamma ray

Three main bands are stronger and 493 extends to 497; Bands at 529 and 635 are more likely to be seen in this direction.

Emission lines

No

Database reference

None yet

Notes

Use a polarizing filter to locate gamma and intensify the three bands