Basic Characteristics of Lapis Lazuli

(1) Chemical formula: (Na, Ca)6(Al, Si)12O24(S, SO4).

(2) Mineral components, the main mineral is lapis lazuli, followed by tremolite, calcite, pyrite, etc., occasionally containing galena and blue galena. It belongs to the family of galena.

(3) Morphology: isometric crystal system, dense massive aggregates, fine-grained - cryptocrystalline structure, particle size from a few thousandths to a few tenths of a millimeter.

(4) Color: indigo, sky blue, light blue and blue-violet, pure dark blue is the best.

(5) physical properties: hardness 5, relative density 2.7 ~ 2.9, without pyrite, relative density of 2.70 or so, with pyrite relative density increased. Brittle, visible fracture, opaque. Lapis lazuli when containing calcite hydrochloric acid blistering, release rotten egg odor (hydrogen sulfide). Lapis lazuli for the dense block has more flaky locks, called the thousand layer plate.

(6) optical characteristics: homogeneous minerals, refractive index 1.50. Lapis lazuli rhombohedral variant of the biaxial crystal minerals, refractive index 1.504 ~ 1.540. This variant in the metamorphic limestone, marble or pegmatite output.

(7) Luminescence: orange spot fluorescence or striped fluorescence under long-wave irradiation of ultraviolet light, and pink fluorescence under short-wave.