Lapis lazuli

Lapis lazuli
A polished specimen of lapis lazuli.
General
Category	Rock
Formula (repeating unit)	mixture of minerals
Identification
Color	Blue, mottled with white calcite and brassy pyrite
Mohs scale hardness	5–5.5
Luster	dull
Streak	light blue
Specific gravity	2.7–2.9
Refractive index	1.5
Other characteristics	The variations in composition cause a wide variation in the above values.

Lapis lazuli is a mineral, and a gemstone. It is formed as a metamorphic rock of the limestone type.

Lapis is famous for its beautiful blue colour: its name means "stone of blue". Lapis Lazuli has been used for many things. Its has been made into beads and used in jewellery since Prehistoric times. It can be carved into statuettes (little sculptures). The major use was as a pigment (colour) in artists' paint. During Medieval and Renaissance times, lapis was ground into powder, and mixed with oil. It was used as the colour for painting the sky, and blue clothes. It can be seen in the fresco paintings of Giotto and the tempera paintings of Fra Angelico.