In 1750, a Parisian jeweller discovered that the yellow Brazilian topaz becomes pink on exposure to a moderate heat, and this treatment has since been extensively applied so that nearly all the pink topaz occurring in jewellery has been heat treated. The source of the pigment ultramarine. It is not a mineral but a rock coloured by lazuite. Lapis lazuli was used in prehistoric times for jewellery. Some palaces and churches have panels and columns inlaid with Lapis.
Lapis lazuli is sensitive to strong pressure and high temperatures.
Turquoise Turquoise means Turkish Stone because the trade route that brought it to Europe came via Turkey. The colour of turquoise ranges from blue to various shades of green to greenish and yellowish gray. A delicate sky blue, which provides an attractive contrast with precious metals, is most valued for gem purposes. Delicate veining, caused by impurities, is desired by some collectors as proof of a natural stone. The stone's colour and luster tend to deteriorate with exposure to sunlight, heat, or various weak acids.