Datolite - Encyclopedia

    Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Monoclinic
    Chemistry : CaBSiO4(OH)
    Rarity : Uncommon

Datolite is a secondary boron silicate of hydrothermal origin. It is a mineral that owes its name to the Greek dateisthai (divide) and lithos (stone) because subjected to a shock the aggregates are easily fragmented. It is generally formed like zeolites and prehnite, in the cavities of basic magmatic rocks, but also as a hydrothermal alteration product in various metal deposits in basic context as well as in skarns and limestones subjected to the action of B-rich fluids. Datolite in developed and aesthetic crystals is rare and usually occurs as tabular crystals ; the mineral is more common in globular, columnar or radiate masses, of porcelain aspect. From vitreous to resinous, it is colorless or pale yellow-green, sometimes white or greyish, pale blue or pale violet. Because of its rarity in aesthetic crystallizations, it is a mineral little known by mineral collectors, it is also a mineral cut for jewelry, especially in cabochons.

Green datolite from Dalnegorsk, Russia
Green datolite from Dalnegorsk, Russia
Orange datolite crystals on a green one from Dalnegorsk, Russia
Yellowish green datolite from Dalnegorsk, Russia

Datolite in the World

The most beautiful crystals in the World come from three deposits : the Lane quarry (Westfield, Massachussets) which produced clear green-white crystals measuring up to 7 cm and Charcas (San Luis Potosi, Mexico), with large greenish crystals of coarsely cubic appearance. The largest known crystals come from Dal'negorsk (Russia) with exceptional pale blue to green crystals of 12 cm (main photo). Large crystals are also known in Virginia (Leesburg) and Canada (Sydenham, Ontario). Original specimens (white decimetric porcelain masses, pink-colored on their edges with fine inclusions of native copper) were extracted from the copper mines at Keweenaw, Michigan (photo on right). In Europe, good specimens have been described in St. Andreasberg (Harz, Germany) and in the serpentinites of the Italian Alps (Baveno, Tiso, etc...).

Datolite in France

In France, datolite is reported at Raon-l'Étape in the Vosges Department in the old quarry of the Pomme de Pin, Côte Saint-Dié, Col of Sainte-Marie-aux-Mines or Wisembach. According to the geologist Daubrée, datolite frequently carpets the druses of kersantites, very frequent in this granitogneissic massif.

Twinning and special crystallizations

There is no known twinning for this mineral species. Although not currently described and because of its formation process, datolite can certainly replace fossils.

Fakes and scams

No fake known for this species.

Hardness : 5 to 5.5
Density : 2.6 to 3
Fracture : Irregular to conchoidal
Streak : White

TP : Translucent to transparent
IR : 1.626 to 1.654
Birefringence : 0.044
Optical character : Biaxial -
Pleochroism : Weak
Fluorescence : None

Solubility : Acids

Magnetism : None
Radioactivity : None


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