Colour

Red in various shades from pinkish to dark purplish red

Cause of colour

Chromium - Allochromatic

Optical Character

Uniaxial negative     

Pleochroism

Distinct – two shades of red

Colour change

No but redder in tungsten

Spectrum; no polar Calibration in nm.

Transmits mainly in red, orange and blue, violet absorbed. Lines at 694/693 may fluoresce. Weak lines at 668 and 659. Broad band centred at 550. Lines at 476/475 and 468.

Ordinary ray

694 stronger; 550 band broader; 475 stronger

Extraordinary ray

694/693 weaker; 668 missing 550 band narrower;

Alpha ray

Not applicable

Beta ray

Not applicable

Gamma ray

Not applicable

Emission lines

Yes at 694/693

Database reference

RDF0756 in RD4 See others in RD2; RD3; RD4 and RD5.

Notes

Natural and synthetic stones show a similar spectrum