October 2009 Mineral of the Month

BENITOITE

Benitoite was first described in 1907 by George D. Louderback, who named it benitoite. "as it occurs near the head waters of the San Benito River in San Benito County, California." It is the California State gemstone.

Benitoite is a rare blue barium titanium silicate mineral found in hydrothermally altered serpentinite and also in schists. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color.

Benitoite is a member of the silicates group. It comes in at a 6-6-1/2 on the Mohs Scale. It has a conchoidal to uneven fracture and an indistinct cleavage. It has a trigonal/hexagonal crystal system with a vitreous luster. Benitoite is typically blue, purple, pink, white, colorless and often multicolored. The stone is transparent to translucent with a colorless streak. Its chemical composition is BaT1Si3O9.

Benitoite is typically found with some combination of natrolite, joaquinite and neptunite on a greenish-gray serpentinite base.

Benitoites' main uses are as collectors' specimens, especially in specimens which show off its commonly associated minerals. Benitoites' hardness also makes it suitable for use as a gemstone, though the general lack of suitable material has limited this use.

September 2009 Mineral of the Month

AZURITE

Its name comes from the Persian word 'Lazhward', meaning 'blue', in reference to its color.

There are over 45 well-known forms, and over 100 forms have been described. Azurite is often pseudomorphed to Malachite, and the two are very frequently found together.
It is a member of the carbonates group and its chemical composition is Cu3+2(CO3)2(OH)2.
It has a perfect cleavage and has a conchoidal fracture. It is a very soft stone coming in at 3-1/2 to 4 on the Mohs Scale. Its specific gravity is 3.77 to 3.78.
This mineral's typical crystal system is monoclinic. It forms as tabular and short prismatic crystals which may be twinned. It also occurs in massive, nodular, stalactitic and earthy habits.
It is usually a rich deep azure blue. The streak is a paler blue. Azurite varies from transparent to opaque and it has a vitreous or dull luster.
Azurite forms in the oxidized regions of copper deposits. It is a secondary mineral formed by the action of carbonated water acting on copper-containing minerals
Azurite is soluable in hydrochloric acid with effervescence. It fuses easily and will turn black when heated.
The intense color of Aurite makes it a popular collector's stone. However, bright light, heat, and open air all tend to reduce the intensity of its color over time. To help preserve the deep blue color of a pristine Azurite specimen, collectors should use a cool, dark, sealed storage environment similar to that of its original natural setting.
Azurite was used as a blue pigment for centuries. Depending on the degree of fineness to which it was ground, and its basic content of copper carbonate, it gave way to a wide range of blue hues.