Datolite

(mineralogy) CaBSiO₄(OH) A mineral nesosilicate crystallizing in the monoclinic system; luster is vitreous, and crystals are colorless or white with a greenish tinge.

A mineral nesosilicate, composition CaBSiO₄(OH), crystallizing in the monoclinic system. It usually occurs in crystals showing many faces and having an equidi-mensional habit. It may also be fine granular or compact and massive. Hardness is 5–5½ on Mohs scale; specific gravity is 2.8–3.0. The luster is vitreous, the crystals colorless or white with a greenish tinge. Datolite is found in the Harz Mountains, Germany; Bologna, Italy; and Arendal, Norway. In the United States fine crystals have come from Westfield, Massachusetts; Bergen Hill, New Jersey; and various places in Connecticut. In Michigan, in the Lake Superior copper district, datolite occurs in fine-grained porcelainlike masses which may be coppery red because of inclusions of native copper. See also Silicate minerals.

Environment

Though not a zeolite, it is often associated with zeolites, in cavities in traprock. Rarely occurs as gangue in ore veins in Michigan, Mexico, and Russia.

Usually in crystals, which may be 2 in. (5 cm) across. Often well formed, more or less equidimensional, but all faces not equally lustrous; some usually dull. Also (in Michigan) in white porcelaneous opaque nodules, round masses of microscopically granular material, commonly stained reddish by iron.

Colorless, light yellow-green, white; fine-grained examples stained reddish. Luster glassy and porcelaneous; hardness 5-5Ɖ; specific gravity 2.8-3.0; fracture conchoidal to uneven, cleavage none. Transparent to translucent.

Alkaline calcium boron silicate (35.0% CaO, 21.8% B ₂ O ₃ , 37.6% SiO ₂ , 5.6% H ₂ O).

Fuses very easily with bubbling to form a viscous, clear glass ball that fluoresces blue in shortwave ultraviolet. Gives green (boron) flame.

In appearance datolite resembles a zeolite, but the green boron flame, with the easy fusibility and moderate swelling (zeolites might be called immoderate), is a certain test.

Fine examples are found in the traprocks of the New England coast, with the sharpest examples coming from the Lane Quarry at Westfield, Massachusetts, in an association with prehnite, babingtonite, and epidote. The best of the Paterson, New Jersey, specimens, from a similar occurrence, are almost as good.

The cluster of small crystals and the spherical gas-cavity fillings of fine-grained material in the Lake Superior copper mines are also good. The fine-grained porcelaneous Michigan datolite, the original find responsible for its name, appears not to be found elsewhere now. Good crystals are found in Andreasberg in the German Harz, in the Italian and Austrian Alps, and in Tasmania. Remarkably large greenish crystals, closely intergrown and poorly individualized, are frequent in the Charcas, Mexico, danburite locality. Clear, pseudo-orthorhombic crystals to 1 in. (2 cm) have been found in the uranium mine near Bancroft, Ontario.

Datolite

Datolite is a calcium boron hydroxide nesosilicate, CaBSiO₄(OH). Datolite crystallizes in the monoclinic system forming prismatic crystals and nodular masses. The luster is vitreous and may be brown, yellow, light green or colorless. The Mohs hardness is 5.5 and the specific gravity is 2.8 - 3.0. The type localities are in the diabases of the Connecticut River valley and Arendal, Aust-Agder, Norway. Associated minerals include prehnite, danburite, babingtonite, epidote, native copper, calcite, quartz and zeolites. It is common in the copper deposits of the Lake Superior region of Michigan. It occurs as a secondary mineral in mafic igneous rocks often filling vesicles along with zeolites in basalt. Unlike most localities throughout the world, the occurrence of datolite in the Lake Superior region is usually fine grained in texture and possesses colored banding. Much of the coloration is due to the inclusion of copper or associated minerals in progressive stages of hydrothermal precipitation.

Botryolite is a botryoidal form of datolite.

References

Wikimedia Commons has media related to: Datolite

• Webmineral
• Mineral galleries
• Mindat

This article about a specific silicate mineral is a stub. You can help Wikipedia by expanding it. v • d • e

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)