Benitoite Visible Spectra (350 - 2000 nm)

Benitoite is a rare, strongly dichroic, blue mineral used as a gemstone  . It is found in significant quantities only near the head waters of the San Benito River, San Benito County, California. In spite of much effort to study benitoite, the origin of color in benitoite has not been definitively established. Because traces of Fe are found in benitoite, ideas proposed include the Fe²⁺ - Ti⁴⁺ or the Fe²⁺ - Fe³⁺ intervalance charge transfer. While most benitoite is colorless when viewed down the c-axis, there is a very small number of exceedingly rare stones (now cut into gemstones) which are pink in this direction. All of the pink stones came from the same small pocket in the mine. Heat and irradiation of blue stones does not change their color. Irradiation of colorless stones does not change their color, but heat treatment can make them turn orange.

• Images of representative benoite spectra

• GRR 561 blue benitoite spectrum; San Benito County, California. 0.997 mm thick.   Or view the expanded visible region; in a slightly less colored zone. Data Files: a; c; 
  
• GRR 562 benitoite spectrum, San Benito County, California. 0.591 mm thick. The spectrum on a wavenumber scale.

• Images of the spectra of unusual benitoite varieties
  

• GRR 303 pink benitoite spectrum; San Benito County, California. It is now a 4.34 mm diameter round faceted stone which appears pink when viewed down the c-axis and blue when viewed perpendicular to the c- axis. The pink color appears in the E||a spectrum.
• GRR 456 pink benitoite spectrum; San Benito County, California. This is the spectrum (in the E||a direction) of the stone with the deepest pink color in existence. It is now a 4.32 mm diameter round faceted stone.
• GRR 1846 orange benitoite spectrum; This is a color variety   of benitoite that forms when colorless stones are heated. The spectrum is presented for a 2.34 mm thick slab.

Link to references on the spectra of benitoite

 Back to the Index of Data Files