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LAPIS-LAZULI.
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present, as well as lime and iron. But it is the presence of sulphur in two forms of combination, namely as sulphide and as sulphate, which distinguishes the blue pigment, obtained by the treatment of lapis-lazuli, from all other blue compounds. This pigment has been very successfully imitated, not only as to colour but as to chemical constituents, by chemical art. It should be added here that the minute brass yellow specks, or spangles which are commonly seen in lapis, are iron pyrites. Lapis was the sapphire of the ancients.

Lapis-lazuli occurs in Transylvania, Siberia, Tartary, Persia, China, Thibet and Brazil. The richly coloured varieties are used for beads and for mosaic work and inlays in bijouterie, vases, furniture, and even in the internal decoration of buildings.

The hardness of lapis-lazuli lies between 5 and 5·5; its specific gravity is about 2·4. By moderate heating the blue colour of this mineral is generally unaffected, though in some cases it may actually be deepened. Carbonic acid does not affect it, nor does a cold weak solution of alum. Strong acids decompose it, the colour disappearing and sulphuretted hydrogen being given off.

The blue mineral called lazulite, although it sometimes presents an appearance slightly resembling that of lapis-lazuli, is not connected with the latter species by chemical constitution, for it is a phosphate, not a silicate (see page 72, under turquoise).

A thin section of lapis-lazuli constitutes a most beautiful microscopic slide. The perfect transparency and superb colour of the blue portions are characteristic. Until thus seen by transmitted light it would not be imagined that a mineral which appears by reflected light to be almost opaque could allow the passage of so much light through it.


Iolite,

Called also dichroite and saphir d'eau, and known to mineralogists as cordierite, is a beautiful and curious stone, remarkable for its