Very Interesting Things: What Is Lapis Lazuli?

Very Interesting Things: What is Lapis Lazuli?

 

Lapis lazuli, also known simply as “lapis,” is a blue metamorphic rock that has been used by people as a gemstone, sculpting material, pigment, and ornamental material for thousands of years. High quality lapis lazuli can be a costly gem. The most desirable specimens have a rich, solid blue color and perhaps a few reflective pieces of gold pyrite.
Unlike most other gem materials, lapis lazuli is not a mineral. Instead, it is a rock composed of multiple minerals. The blue color of lapis lazuli is mainly derived from the presence of lazurite, a blue silicate mineral of the sodalite group with a chemical composition of (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2.

Geologic Occurrence of Lapis Lazuli
Lapis lazuli forms near igneous intrusions where limestone or marble has been altered by contact metamorphism or hydrothermal metamorphism. In these rocks, lazurite replaces portions of the host rock and often preferentially develops within certain bands or layers.
Afghanistan is the world’s leading source of lapis lazuli. Some parts of the country have been actively mined for thousands of years. Other countries that produce notable amounts of lapis lazuli include Chile, Russia, Canada, Argentina, and Pakistan. In the United States small amounts of lapis lazuli have been produced in California, Colorado, and Arizona.

Physical Properties of Lapis Lazuli
Classification A metamorphic rock that contains enough of the mineral lazurite to impart a distinct blue color. It may also contain significant amounts of calcite, pyrite, and minor amounts of other minerals. Color Blue. Often with white calcite veining or mottling, and gold grains of pyrite. Streak Blue. Luster Dull, but polishes to a bright luster. Diaphaneity Semi-translucent to opaque. Cleavage None, though it may split easily along foliation or calcite veins and layers. Mohs Hardness Varies between the 3 of calcite and the 5 to 5.5 of lazurite. Not well suited for use as a ring stone or in bracelets. Specific Gravity 2.7 to 2.9 or more depending upon the amount of pyrite Diagnostic Properties Blue color, association with pyrite, and hardness. Uses Cabochons, beads, carvings, spheres, inlay, and pigments.

Composition and Properties of Lapis
In addition to lazurite, specimens of lapis lazuli usually contain calcite and pyrite. Sodalite, hauyne, wollastonite, afghanite, mica, dolomite, diopside, and a diversity of other minerals might also be present. To be called “lapis lazuli,” a rock must have a distinctly blue color and contain at least 25% blue lazurite.

Calcite is often the second most abundant mineral present in lapis lazuli. Its presence can be very obvious, appearing as white layers, fractures, or mottling. It can also be finely intermixed with lazurite to produce a rock with a faded denim color.
Pyrite usually occurs in lapis lazuli as tiny, randomly spaced grains with a contrasting gold color. When abundant, the grains can be concentrated or intergrown into distinct layers or patches. It can occasionally occur as a fracture-filling mineral.
As a rock, lapis lazuli is composed of several minerals, each with its own hardness, cleavage/fracture characteristics, specific gravity, and color. Hardness ranges from a Mohs 3 for calcite to the 6.5 of pyrite. The hardness of the material depends upon where you test it.

Lapis Lazuli History
Lapis lazuli has been popular through most of recorded human history. Mining for lapis occurred in the Badakhshan Province of northeastern Afghanistan as early as 7000 BC. The lapis was used to make beads, small jewelry items and small sculptures. These have been found at Neolithic archaeological sites dating back to about 3000 BC in Iraq, Pakistan, and Afghanistan.
Lapis lazuli appears in many Egyptian archaeological sites that date back to about 3000 BC. It was used in many ornamental objects and jewelry. Powdered lapis was used as a cosmetic and a pigment.
In Biblical times the word “sapphire” was often used as a name for lapis lazuli. For that reason, many scholars believe that at least some of the references to sapphire in the Bible are actually references to lapis lazuli. Some modern translations of the Bible use the word “lapis” instead of “sapphire.”
Lapis lazuli started to be seen in Europe during the Middle Ages. It arrived in the form of jewelry, cutting rough, and finely ground pigment.
Today lapis lazuli is still used in jewelry and ornamental objects. As a pigment it has been replaced with modern materials except by artists who strive to use historical methods.

Lapis Lazuli as a “Conflict Mineral”?
Afghanistan has been one of the world’s primary sources of lapis lazuli through most of recorded history. Most of the country’s production comes from thousands of small mines in the Badakhshan Province. This is an area with a destitute economy, where opium poppy growing and gemstone mining are the only important sources of outside revenue.
Much of the area where the lapis lazuli mining occurs is occupied by the Taliban and local members of the Islamic State. They operate illegal mines, attack other mines to capture
their production, and demand protection payments from intimidated mine operators. Revenue from these activities is used to fund war and terrorism.
Numerous advocacy groups and some members of the Afghanistan government would like to see Afghanistan’s lapis lazuli classified as an international “conflict mineral.” This would require the country’s government to track the production and sale of lapis lazuli from mine to market. It would also involve an international effort to keep illicit lapis lazuli from being traded. The Kimberly Process, used for tracking the flow of diamonds, would serve as a model for the tracking of illicit lapis lazuli.

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