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Benitoite
From Wikipedia, the free encyclopedia
| Benitoite | |
|---|---|
 Benitoite on natrolite
|
|
| General | |
| Category | Mineral |
| Chemical formula | BaTiSi3O9 (barium titanium silicate) |
| Identification | |
| Color | Blue; Colorless |
| Crystal habit | Tabular dipyramidal crystals, granular |
| Crystal system | Hexagonal |
| Cleavage | [1011] Poor |
| Fracture | Conchoidal |
| Mohs Scale hardness | 6 - 6.5 |
| Luster | Vitreous |
| Refractive index | 1.757-1.759; 1.802-1.804 |
| Pleochroism | Dichroic (blue to white) |
| Streak | White |
| Specific gravity | 3.6 |
| Solubility | Insoluble: HCl, H2SO4 Soluble: HF |
| Diaphaneity | Transparent to translucent |
Benitoite, whose name derives from its type locality (San Benito County, California) is a blue silicate mineral, found in hydrothermally altered serpentinite. Benitoite fluoresces under ultraviolet light, appearing light blue in color.
Contents |
Benitoite's rarity makes it a minor ore for barium or titanium at best. Rather, benitoite's main uses are as collector's specimens, especially in specimens which show off this mineral's unique crystals, or specimens in which benitoite occurs with its commonly associated minerals. Benitoite's hardness also makes it suitable for use as a gemstone, though the general lack of usable material has limited this use.
Benitoite typically occurs with an unusual set of minerals, along with minerals that make up its host rock. Frequently associated minerals include:
| natrolite | Na2Al2Si3O10 · 2H2O |
|---|---|
| neptunite | KNa2Li(Fe, Mn)2Ti2Si8O24 |
| joaquinite | NaBa2FeCe2(Ti, Nb)2(SiO3)8(OH, F) · 1H2O |
| serpentine | (Mg, Fe)3Si2O5(OH)4 |
| albite | NaAlSi3O8 |
Benitoite is a rare mineral, found in very few locations, most prominently in the Dallas Gem Mine in San Benito County, California, but also in Japan and Arkansas. Finding a blue mineral in these locations is a useful first step in identifying benitoite, but some key attributes should be kept in mind. First, benitoite's crystal habit is unusual, and would make a strong aid to identification. The associated minerals are also a key piece of information. Benitoite is typically found with some combination of natrolite, joaquinite, and neptunite on a greenish-grey serpentinite base. Finally, benitoite's fluorescence is used for identification purposes.
Benitoite is the official state gem of California (California Geologic Survey).
Benitoite is the official gem of E Clampus Vitus.
- Mineral Resources, California Geologic Survey. Accessed December 31, 2005
- WebMineral Listing
- MinDat Listing
- Mineral Galleries
- Friends of Mineralogy review of benitoite