Lapis lazuli is a deep-blue, opaque material valued for its intense color and historical significance for millennia. Technically a metamorphic rock, it is an aggregate of several minerals formed under heat and pressure. Its characteristic color and scarcity have made it a commodity since ancient times, featuring prominently in historical artifacts and art. It is found in only a few geological settings worldwide.
Defining the Mineral
Lapis lazuli’s vibrant blue shade is derived primarily from the mineral lazurite, which typically makes up between 25% and 40% of the rock’s composition. Lazurite is a complex sulfur-containing silicate of the sodalite mineral group. The presence of sulfur produces the material’s distinctive hue.
The lapis structure is visually defined by its other mineral components, which contribute to its overall appearance and grade. The rock often contains white streaks or patches of calcite, which is a calcium carbonate mineral. The golden flecks scattered throughout the deep blue background are inclusions of pyrite, or iron sulfide.
Geological Formation
The formation of lapis lazuli requires a specific geological process known as contact metamorphism. This process begins when an intrusion of hot magma comes into direct contact with a pre-existing body of calcium-rich rock, such as limestone or dolomite. The intense heat and chemical activity from the magma alter the surrounding rock without melting it completely.
The chemical reaction requires the original rock to be subjected to high temperatures and relatively low pressure. This alteration introduces new elements and causes the limestone to recrystallize, forming the new mineral lazurite. The resulting lapis lazuli is found within veins or lens-like bodies in the surrounding marble.
The Ancient Source of Supply
For over 6,000 years, the most productive source has been the Sar-e-Sang mines, located in the Hindu Kush mountains of the Badakhshan province in northeastern Afghanistan. These ancient mines, situated in the Kokcha River valley, are one of the world’s oldest continuously exploited gem deposits. The lapis lazuli extracted from this region is consistently regarded as the highest quality material due to its saturated, uniform color and minimal calcite inclusions.
This Afghan source supplied all of the major ancient civilizations, becoming a trade commodity along routes that stretched into Mesopotamia, Egypt, and the Indus Valley. The material was highly valued and used for the inlay in Egyptian pharaoh Tutankhamun’s gold funerary mask, dating back to the 14th century BCE. Even today, the Sar-e-Sang mines remain the primary global source for the finest royal blue lapis lazuli.
Modern Global Deposits
While Afghanistan remains the historical and quality standard, other geological settings around the world contain lapis lazuli deposits that contribute to the modern global supply. The Andes Mountains in Chile are home to the most significant secondary source, particularly in the Ovalle area. Chilean lapis often presents a lighter blue color and typically contains a greater proportion of white calcite veining compared to the Afghan material.
The Tultui lazurite deposit is found in the Lake Baikal region of Siberia, Russia. This deposit produces a deep blue material, sometimes rivaling the Afghan grade, but the output is not commercially significant. Minor deposits have been identified in other locations, including Pakistan and occurrences in the United States, such as in the mountains of Colorado.