The chief constituent is 'azurite, or silicate of sodium and aluminum containing sulphur, Na8S(Al02),(Si02)6, but the synthetic product also contains an abnormally large amount of sodalite. It is manufactured from an agglomeration of artificial raw materials by a process similar to that used for ceramics and apparently corresponds only very approximately to the composition of natural lapis lazuli, which is in any case somewhat variable, being a rock.
Cubic, for both lazurite and sodalite
In bars obtained from a mould, of a uniform deep blue color with an almost violet tinge. Some are dot-ted with minute, evenly distributed pyrite crystals.
It has a hardness of 4.5, therefore a bit lower than that of natural lapis lazuli. The refractive index is about 1.50. The density is 2.38-2.46 g/cm3, thus slightly lower than that of natural lapis lazuli, although roughly the same as that of its chief constituent, lazurite. It is distinctly porous.
Synthetic lapis lazuli
This is not yet widely available on the market. Appearance A uniform, deep blue color with a hint of violet, which is uncommon in the natural material. It easily takes a fine polish and is also produced scattered with minute fragments of pyrite. It is made into cabochons and, above all, spherical or polyhedral polished necklace beads.
It never contains the patches and veins of light-colored minerals often visible in natural lapis lazuli. Because this product is an artificial agglomerate of tiny, relatively homogeneous particles, rather than a collection of small crystals which have developed together, interpenetrating to some extent, granulometry reveals a minute, uniform structure. Furthermore, when synthetic lapis lazuli contains pyrite, microscopic examination reveals that this consists of small, ground fragments evenly mixed with the other constituents. It reacts to hydrochloric acid by an even stronger emission of hydrogen sulphide than natural lapis lazuli. The combination of unusually low density and high porosity is quite distinctive.
Decidedly low, much likes that of other inexpensive synthetic ornamental materials.
Writer – Curzio Cipriani & Alessandro Borelli