In the gemstone industry, Lapis Lazuli is unique because it is not a single mineral, but a rock. While most gemstones are defined by a specific crystal lattice, Lapis is a metamorphic rock composed of several different minerals fused together under intense heat and pressure.
To understand the “Lapis Lazuli family,” one must look at the specific mineral components that dictate its quality and market value.
1. The Mineral Composition For a specimen to be classified as Lapis Lazuli, it must contain a high concentration of Lazurite. However, a high-quality stone is a balance of the following three primary minerals: Lazurite: The essential component. It is a complex blue silicate ($Na,Ca)_8(AlSiO_4)_6(SO_4,S,Cl)_2$. This mineral provides the intense royal blue color. Calcite: Appears as white veins or “clouds.” In the trade, excessive calcite significantly lowers the value as it dilutes the blue saturation.
Pyrite: Often called “Fool’s Gold.” These are brassy, metallic inclusions ($FeS_2$). In moderate amounts, gold-flecked pyrite is the hallmark of authentic Lapis Lazuli.
2. Technical Grade and Classification The “family” is generally graded based on the origin and the ratio of these minerals. Unlike other gems, Lapis is often categorized by its geographic “type” because the geology of the mine dictates the look: Persian (Afghan) Type: The highest grade. It is characterized by an intense, uniform, dark violet-blue with little to no visible calcite and a light scattering of pyrite. Russian (Siberian) Type: Usually features a very dark blue but is often heavily “speckled” with pyrite.
Chilean Type: Frequently contains a high percentage of Calcite, appearing as a lighter, “denim” blue with white mottling.
3. The Geological Origin: Contact Metamorphism Lapis Lazuli forms through contact metamorphism. This occurs when hot magma intrudes into limestone or marble deposits. The heat from the magma “cooks” the limestone, and the chemical exchange between the two materials creates the lazurite.
This explains why Lapis is found in such rugged, inaccessible terrains—primarily the Hindu Kush mountains of Afghanistan. These mines have been active for over 6,000 years, making Lapis one of the oldest traded commodities in human history.
4. Physical and Chemical Properties Because it is a rock (a mixture), its properties vary slightly depending on the mineral ratios: Property Technical Value Primary Mineral Lazurite Mohs Hardness 5.0 – 5.5 (Relatively Soft) Refractive Index Approximately 1.50 (Variable) Specific Gravity 2.40 – 2.90 Luster Vitreous to Greasy
5. Practical Handling and Durability From a practical standpoint, Lapis Lazuli is a porous material.
Sensitivity: It is highly sensitive to acids and chemical solvents. For a “Mine-to-Market” company, this is crucial: raw Lapis should never be cleaned with harsh chemicals.
Dye Detection: Because lower-grade Lapis is often dyed to look like “Persian” grade, your vertical integration is a major selling point. Sourcing directly from the mine ensures the stone’s color is natural and not a surface treatment.
