Benitoite

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Benitoite
Benitoite on natrolite
General
Category	Mineral
Chemical formula	Ba Ti Si₃O₉ (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.

1 Uses of benitoite
2 Associated minerals
3 Notes for identification
4 Trivia
5 References

[edit] Uses of benitoite

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 useable material has limited this use.

[edit] Associated minerals

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	K Na₂Li(Fe, Mn)₂Ti₂Si₈O₂₄
joaquinite	Na Ba₂Fe Ce₂(Ti, Nb)₂(Si O₃)₈(OH, F) · 1H₂O
serpentine	(Mg, Fe)₃Si₂O₅(OH)₄
albite	Na Al Si₃O₈

[edit] Notes for identification

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.