Otherwise known as just 'Lapis'
The beautiful blues in paintings from the Renaissance are thanks to the blue of lapis lazuli, the opaque blue gem material that was the secret ingredient in ultramarine, the valuable pigment that all the old masters used to capture the rich blues of the sea and sky and the robes of the Virgin Mary. The color wasn't duplicated by any other substance until 1834 but even now, some argue there is no substitute: unlike other pigments ultramarine centuries old still glows with rich color today.
As befits a gem that has been international currency for millennia, the name lapis lazuli is mélange of languages. From the Latin, lapis means stone. From the Arabic, azul means blue. More information on Lapis Lazuli can be found here. 
FACTS
MINERAL: Rock
CHEMICAL COMPOSITION: An aggregate
COLOR: Greenish blue to violetish blue
REFRACTIVE INDEX: 1.500, sometimes 1.670
BIREFRINGENCE: None
SPECIFIC GRAVITY: 2.75 (+/- 0.25)

-Source AGTA, GIA