Lapis lazuli

The lapis lazuli is a metamorphic Roche, containing Silicate S of the group of the Feldspath S. It is especially known like decorative, opaque stone, of color Bleu E, between the azure and the overseas. Its use is very old, tonic with 7  000 years. The name derives from Latin lapis lazuli , who mean stone, and from the Perse, لاژورد lajevard , which means blue.

Characteristics

The lapis lazuli is made up mainly of Lazurite (25 with 40  %), mineral made up of Sodium, Aluminum, Silicon, Oxygen and Sulfur.

It contains generally also Calcite (white), Sodalite (blue) and Pyrite (yellow).

Its chemical formula is (Na, Ca) (Al, If) OS FeS- CaCO.

One often finds it in the Calcaire, where it changes by metamorphism of contact.

The lapis lazuli of value have an intense blue color, strewn with yellow pyrite glares. If the latter are too numerous, or if the stone contains white calcite veins, then it loses its value.

Use

Lapis lazuli can be perfectly polished and it is largely used in jewelry. One also makes use of it to manufacture mosaics, sculptures and various ornaments.

Crushed, it was used as blue pigment (Outremer) for painting Tempera (and sometimes also for the oil-base paint). This use ceased at the beginning of the 19th century by the introduction of pigments of synthesis, sometimes called overseas Frenchwoman.

Lapis lazuli can be artificially improved by the addition of dyes, waxes or resins. The spinel , another decorative stone, was sometimes sold for lapis lazuli. Other imitations, purely synthetic are also found, of which some contain pyrite spots but not calcite. Certain types of plastics or glasses can also pass for lapis lazuli.

History

In the Antiquity, one confused lapis lazuli and Saphir. Thus, Pline speaks about sapphire with gilded spots. One finds references similar in the Bible.

In the ancient Egypt, lapis lazuli was one of the preferred decorative stones, to carve amulets (in particular beetles). The Babylonian and the Assyrie NS also made use of it to manufacture seals. At that time, the mines were located in the Badakhshan, in the north of the Afghanistan.

During the Roman epoch, lapis lazuli had the reputation to be a Aphrodisiaque.

With the the Middle Ages, other virtues médicinales  were allotted to him;: good for the robustness of the members, and preventing the spirit of the fear, the doubt and the desire. It was drunk crushed, mixed with milk.

Layers

The principal layers are located in Afghanistan, with the Badakhshan. Those of the Chile, to Oval, provide a paler stone. One also finds some in other countries, in moindre  quantity;:

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