Lapis lazuli blue

Lapis lazuli is a vibrant blue rock that is an aggregate of hauynite (which contributes the rich blue colour), sodalite (also blue), noselite and lazurite (an isomorphous combination of hauynite and sodalite). It also generally contains calcite and iron pyrite. For centuries it was ground into a fine powder and made into a highly prized (and expensive) blue pigment whose use was closely controlled by the Catholic church. The Venetians - who ran this trade - eventually broke this stranglehold and the paint was used for more than just the virgin Mary's cloak. Giotto was a great user of ultramarine blue!

Synthetic "French ultramarine" became an affordable alternative in the early 19th century.

The top (light blue line) spectrum comes from the sample in the photograph. The lower spectrum (dark blue) is from a polished stone from Pakistan. The fluorescence spectrum (red line) shows the typical 'disulphide vibronic ripple' from sodalite.

The deep blue colour of lazurite arises from the presence of sulphur in the form of a polysulphide consisting of three sulphur atoms with a single negative charge. It is the charge transfer between orbitals that produces the strong, broad absorption band at 600nm seen in the reflection spectra above. The fluorescence spectrum, however, comes from disulphide: two sulphur atoms again with a single negative charge.

For this photograph, the rock was illuminated with a 6500K LED which somewhat enhances the blue colour.


Flickr page for this photo.

Visit the Eye for Science Flickr group.

Get the "Eye for Science" widget here and install it on your own blog. Spread the scienticity!

Like this image? Want it for your smartphone wallpaper?
Use this QR Code to load it on your smartphone and enjoy!