Benitoite

'California blue diamond' - state gemstone of California in 1985. Rare and found in significant gem quality quantity only at the head of the San Benito River in California. First discovered in 1907.

Often found with benitoite is a white natrolite bed, opaque and shinny. Also called 'needle zeolite'. Clusters in radiating sprays. Large crystals are long, squared prisms capped with low pyramids. Often dissolved away with an acid to expose the gemstone crystals but with pieces intended for the specimen market some of the natrolite will be preserved to provide a contrasting white background to the blue benitoite.

Also found with black neptunite - well formed prismatic rod-like crystals are square in cross section with pointed terminations. Chemically complex. Not as rare as benitoite and found elsewhere. California type has high iron content. Other types can have high manganese eg: Mt St Hilaire, Quebec or Russian Kola Peninsula. is piezoelectric - generates an electric charge in response to mechanical stress and pressure, with only 2% showing this, particularly quartz. Rarely used as faceted stones due opacity, brittleness and softness (Mohs' 5-6). edges shine a deep red under bright light. Produces reddish streak.

Benitoite crystal form is ditrigonal-dipyramidal, tips flat. Mohs' 6-6.5. When cut stones are more refractive than diamonds.