HAUYNITE 445 



Lapis-lazuli is used much more frequently for small articles, such as letter-weights, 

 candlesticks, bowls, vases, and fancy articles of various kinds, than it is as a gem. Such 

 articles were formerly very expensive, since each was cut out of a single piece of material, 

 and rough blocks of good quality and sufficient size for the purpose are rare. Now such 

 objects are made of metal and veneered with thin plates of lapis-lazuli. The mineral is 

 used also as a decorative material in very ornate buildings, such as the Winter Palace at 

 St. Petersburg and the Castle of Tsarkoe-Selo, in which there are rooms which are 

 wainscotted with lapis-lazuli. The stone is also utilised in mosaics and for inlaying, the 

 yellow, shining specks of iron-pyrites being made to represent stars in a blue sky. Pliny 

 compared the stone to the star-bedecked firmament ; and the shining metallic flecks of iron- 

 pyrites do contrast in fact very effectively with the dark blue background of the stone itself. 



Formerly lapis-lazuli had a very important technical application as a pigment. Uark- 

 coloured fragments of the mineral were powdered up, the blue constituent separated as far 

 as possible from the colourless portions, and the blue powder thus obtained worked up into 

 a paint known to artists as ultramarine. This was the only fine blue pigment known, and 

 was comparatively costly. It is now replaced by an artificial substance which very closely 

 resembles the ultramarine of nature in colour, chemical composition, and other characters^ 

 and which is much lower in price. 



There are certain opaque blue stones and artificial substances which it is possible to. 

 mistake for lapis-lazuli, and which are occasionally passed off as such. Very close imitations 

 of lapis-lazuli can be made in glass, but the colour is less intense ; the specific gravity is 

 higher, and on the smallest broken surface the bright conchoidal fracture of glass can 

 always be seen, as distinct from the dull uneven fracture of true lapis-lazuli. Again, 

 agate is sometimes artificially coloured and sold in the trade as lapis-lazuli ; the colour 

 imparted to such stones is always a dark Berlin-blue and not the deep azure-blue of the 

 genuine stone. Moreover, both the hardness and the specific gravity of agate are 

 greater than those of lapis-lazuli. The blue mineral chessylite or azurite, a hydrated basic 

 copper carbonate, is sometimes substituted for lapis-lazuli ; this is softer and much heavier 

 (sp. gr. = 3'8) than the latter, and is readily and completely dissolved with effervescence in 

 hydrochloric acid. Turquoise is too light in colour to be mistaken for lapis-lazuli, and the 

 blue mineral lazulite does not resemble it closely enough to admit of the one being 

 substituted for the other. 



HAUYNITE. 



This mineral has already been mentioned as one of the coloured constituents of lapis- 

 lazuli. It occurs also in small irregular grains in certain volcanic rocks, and, far more 

 rarely, as regular crystals which have the form of the rhombic dodecahedron. The 

 principal localities are : the neighbourhood of the Laacher See, near Andernach on the 

 Rhine (Niedermendig, &c.) ; the Albanian Hills, near Rome (San Marino, &c.) ; and the 

 French Auvergne. Pure haiiynite is sometimes of a beautiful blue colour, and almost 

 perfectly transparent ; when this is the case it may be cut as a gem, and then commands a 

 fair price. It is said to be worn to a certain extent in France, but it has no importance 

 whatever in the trade. 



Haiiynite, whether in crystals or in grains, has a definite cleavage parallel to the faces 

 of the rhombic dodecahedron. It is translucent to transparent and singly refracting ; its 

 hardness is 5^ and its specific gravity 2"4. These characters serve to distinguish it from 

 all other blue stones. 



