Lazurite

Chemical formula: Na<sub>7</sub>Ca(Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>)(S<sup>6+</sup>O<sub>4</sub>)(S<sub>3</sub>)<sup>1-</sup>·H<sub>2</sub>O

Lazurite is a mineral from the sodalite group with an intense blue color, being the main component of the ornamental rock lapis lazuli.

## Characteristics Lazurite is a tectosilicate from the sodalite group, known primarily as a key component of the metamorphic rock lapis lazuli. It rarely forms well-developed crystals, most often occurring as compact, granular aggregates. Its most characteristic feature is an intense, uniform color in shades from azure to deep ultramarine blue. ## Physical Properties The mineral's hardness is 5-5.5 on the Mohs scale, making it relatively soft. It has a vitreous luster, and on fresh fractures, it can be slightly greasy. It is an opaque mineral, only translucent in thin splinters. Its density ranges from 2.38-2.45 g/cm³. ## Colors and Varieties The dominant and essentially only color of lazurite is a deep, saturated blue, often with a violet hue. The mineral's name comes precisely from its color. No distinct color varieties are recognized, however, it is responsible for the color of lapis lazuli, which is often incorrectly referred to as a "variety" of lazurite in trade. ## History and Name The name comes from the Persian word *lāzhuward* (blue), which through Arabic and Latin entered scientific terminology. Lazurite, as a component of lapis lazuli, was valued since antiquity in Mesopotamia, Egypt, and Rome, where it was used to make jewelry and ornaments. Ground into a powder, it constituted a valuable natural pigment - ultramarine. It was described as a separate mineral species in 1890. ## Applications The main application of lazurite is its role as a component of the ornamental stone lapis lazuli, used in jewelry and sculpture. Historically, it was an indispensable source of the luxurious painting pigment, ultramarine, before its synthetic counterpart was developed in the 19th century.

Properties

Mohs hardness
5-5.5
Luster
Vitreous to Greasy
Streak
Light Blue
Density
2.38-2.45
Cleavage
Poor on {110}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Cubic

Diagnostic features

## Identification The most important diagnostic feature is its intense, uniform blue color. In lapis lazuli rock, it is often accompanied by white calcite veins and golden pyrite inclusions. In contact with hydrochloric acid, it reacts slowly, releasing the characteristic smell of hydrogen sulfide. ## Distinguishing from Similar Minerals - **Sodalite**: Often confused with lazurite, but usually has a lighter, often grayish or purplish shade of blue and often occurs as mottled aggregates with white. Sodalite usually exhibits orange fluorescence under UV light, which lazurite lacks. - **Azurite**: Has a different, more "royal" shade of blue, is heavier, and much softer (3.5-4). As a copper carbonate, it reacts violently (effervesces) with acids and often co-occurs with green malachite. - **Dumortierite**: Usually occurs as fibrous inclusions in quartz, is much harder (7-8.5), and has a slightly different shade of blue. ## Crystal Forms Well-developed crystals are rare and take the form of rhombic dodecahedra. Most commonly, it is found as compact, granular, or massive aggregates.

Geological environment

## Genesis It forms as a result of contact metamorphism of carbonate rocks (limestones or dolomites) under the influence of magmatic intrusions, most often syenitic or granitic. ## Mineral Associations It most often co-occurs with calcite and pyrite (forming lapis lazuli), as well as with diopside, forsterite, haüyne, and sodalite. ## Localities The most famous and historically important deposits in the world are located in the Sar-e-Sang district in Badakhshan province, Afghanistan. Other known localities include the Lake Baikal region in Siberia (Russia), the Vesuvius volcanic complex (Italy), as well as Chile (Andes) and the USA (San Bernardino Mountains in California).

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued specimens are those with a deep, uniform ultramarine color, with a minimal amount of white calcite. The presence of well-developed, though extremely rare, crystals on a rock matrix significantly increases the specimen's value. In the case of lapis lazuli, an even distribution of fine, golden pyrite inclusions is desirable. ## Popular Localities Specimens from Afghanistan (Sar-e-Sang) are considered the global standard of quality and represent the most sought-after collectible and jewelry material. Specimens from Russia (Baikal region) also have historical significance.

Care and storage

## Cleaning Specimens should be cleaned gently, preferably dry with a soft brush or cloth. If necessary, lukewarm water with a small amount of mild soap can be used, then rinsed thoroughly and dried immediately. Ultrasonic cleaners should be avoided. ## What to Avoid Lazurite is very sensitive to acids, which cause discoloration and release of hydrogen sulfide (rotten egg smell). It should be protected from high temperatures, sudden pressure changes, and contact with chemicals. Due to its low hardness, it is susceptible to scratches. ## Storage It is recommended to store specimens separately, wrapped in soft material, to avoid scratches from harder minerals. Although stable, prolonged exposure to direct sunlight should be avoided.

External references

Sources

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