Benitoite has an appearance that is very similar to sapphire. Its blue color and pleochroism are very much like sapphire’s. Benitoite and sapphire have overlapping refractive indices, but benitoite has a much higher birefringence, which often shows birefringence blink.
Sapphire has a Mohs hardness of 9, while benitoite is much softer at 6 to 6.5. Benitoite has a specific gravity of 3.65, compared to a specific gravity of 3.9 to 4.1 for sapphire. Benitoite is usually found in association with other rare minerals, which include natrolite, joaquinite and neptunite.
| Physical Properties of Benitoite | |
| Chemical Classification | Barium Titanium Silicate |
| Color | Most specimens are violetish-blue. Some specimens are colorless. A range of color and saturation between colorless and deep violetish-blue occurs. Rare orange heat-treated specimens are known. |
| Streak | White |
| Luster | Vitreous |
| Diaphaneity | Transparent to translucent |
| Cleavage | Poor |
| Mohs Hardness | 6 to 6.5 |
| Specific Gravity | 3.6 |
| Diagnostic Properties | Tabular dipyramidal crystals. Intense blue fluorescence under short-wave ultraviolet light. Associated with serpentine and albite, but more importantly with rare minerals such as natrolite, joaquinite, and neptunite. |
| Chemical Composition | BaTiSi3O9 |
| Crystal System | Hexagonal |
| Uses | Gemstone, collector mineral, Official State Gem of California. |