INTRODUCTION LAPIZ LAZULI
The ancients knew lapis lazuli as ‘Sapphire’ and it was not until the Middle ages that blue corundum took over the use of that name. All the properties of a cure for diseases of the eye previously claimed for lapis lazuli were then transferred over to the more valuable gem, Sapphire.
Lapis lazuli is, in fact ,a mixture of different minerals: lazurite, hauynite, noselite, sodalite, calciteand pyrite. The best quality contains the least calcite and is found in Afghanistan and Russia. Lapis lazuli is also found in Chile but tends to be paler, containing bands of calcite and generally lacking the specks of golden pyrite that add to the attraction. It is also sourced from Burma (Myanmar) and the USA.
Up until 1828 this beautiful blue mineral was crushed by artists to provide the pigment for ultramarine used for their paint: this is now produced synthetically.Lapis lazuli is often used for signet rings and cufflinks, though with a rating of only 5 ½ on the Mohs scale it can easily be scratched.Paler lapis is dyed to improve the colour but it is not necessarily stable. It is often waxed to improve the polish .The quarts mineral jasper is also dyed and called ‘Swiss Lapis” or ‘German Lapis’.
A synthetic sintered Spinel, containing cobalt and which may contain gold specks , is produced in Germany to simulate lapis lazuli ; it shows bright red under the Chelsea Filter where real lapis shows dull brownish-red. Gilson also produced a synthetic Lapis Lazuli.
LAPIS LAZULI GEMSTONE PROPERTIES
|Composition||Rock made primarily of lazurite (Na, Ca)8(Al, Si)12O24(S, SO4). Also contains haüyne, sodalite and nosean, which are all members of the sodalite group.|
|Hardness (Mohs)(Mohs)||Variable. Generally 5–6|
|Specific Gravity||Variable. Generally 2.7–2.9|
|Refractive Index||ca. 1.50|
|Crystal System||None (lapis is a rock). Lazurite, the main constituent, is isometric, and frequently occurs as dodecahedra.|
|Colors||Blue, mottled with white calcite and brassy pyrite|
|Handling||Due to its softness, care must be taken in the wearing of lapis lazuli.|
|Enhancements||Frequently dyed or impregnated|