Lapis lazuli

Lapis lazuli is treasured for its beautiful deep blue color. The English word azure, French azur, the Italian azzurro,the Polish lazur, Romanian azur and azuriu, and the Portuguese and Spanish azul, Hungarian azúr all come from the name and color of lapis lazuli. 

Lapis Lazuli Treatments:-

                                                Heating to red heat has been reported (Bauer, 1968) to intensify the color of some pale blue lapis lazuli to yield a fine, dark blue, but this may produce an unattractive greenish blue in some specimens.
Dyeing, often using aniline dyes, is frequently practiced to improve the color of lapis lazuli, although even almost colorless material has been so treated (Crowningshield, 1967). Coloring for the disguising of white calcite inclusions is also done. Localization of the color in cracks can usually be seen, and a cotton swab soaked in acetone or nailpolish remover usually reveals the dye. This may not work, however, if a colorless wax has been used as a final step, in which case it must first be rubbed off (Crowningshield, 1968; Fryer, 1981); the wax is revealed by a hot-point examination. The colorless wax is apparently intended to hide cracks, improve the surface polish, as well as to prevent the dye from rubbing off onto clothes or skin.
The use of colored waxes (including blue shoe paste!) has also been reported (Crowningshield, 1965) – Nassau (1984)

Often impregnated with wax or oil. Dyed: Calcite masked. Streak: dark blue (if not coated). Diluted acid test (acetone usually not conclusive) - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 8

Significant Gem Localities:- 

Lapis lazuli has been mined in Afghanistan and exported to the Mediterranean world and South Asia since the Neolithic age. 

In addition to the Afghan deposits, lapis is mined in Russia, Chile, Italy, Mongolia, United States, Canada, Angola, Argentina, Burma, Pakistan, Canada, India.

 Mohs hardness 5 - 5.5