426 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



no specially fine lustre after polishing ; its application as an ornamental stone depends, 

 therefore, solely upon its colour, and the deeper and purer this colour is the more highly is 

 the stone prized. This feature of amazon-stone is supposed by some to be due to the 

 presence of a small amount of copper, but according to other authorities it depends on the 

 presence of organic matter. 



Amazon-stone is a potash-felspar. It is found in irregular masses as a constituent of 

 granitic, syenitic, and similar rocks ; also as regularly developed crystals, which may reach 

 ^ length of 25 centimetres, in magnificent druses, in the crevices and fissures of rocks of the 

 same kind. Fig. 1 of Plate XVI. illustrates the latter mode of 

 occurrence, and a single crystal is represented in Fig. 81. The physical 

 characters of amazon-stone are the same as those of other felspars. Its 

 specific gravity, in correlation with the chemical composition, is some- 

 what low, varying between 2'55 and ^'66. 



The name amazon-stone was first given in the middle of the 

 eighteenth century to a green stone from the Amazon river in South 

 America. It appears to be doubtful whether this was the same sub- 

 stance as that to which the name now refers ; more probably it was 

 nephrite, jadeite, or some other green mineral, for nothing is known 

 at the present day of the occurrence of verdigris-green felspar in this 

 Fig 81. Crystalline • j^ j^ j^ ^ ^^ occur in the Ural Mountains ; here it is 



torm or amazon-stone. o 



found in compact masses near Miask on the eastern side of Lake 

 Ilmen as beautiful crystals associated with topaz and other minerals in granitic rocks. It 

 was met with later at a few places in North America ; of these occurrences the most 

 beautiful is that of Pike's Peak in Colorado. Here it often takes the form of fine crystals, 

 such as are represented in Plate XVI., Fig. 1 ; they are enclosed with grey quartz and 

 flesh-red felspar in a coarse-grained granite. Amazon-stone of a fine colour also occurs in 

 the coarse-grained granite of Allen's mica mine, near Amelia Court House in the State of 

 Virginia, from whence have been obtained hundreds of tons of cleavage fragments, ranging 

 up to 6 and 8 inches in length and of a magnificent green colour. 



Amazon-stone is usually cut in the form of an oval or circular plate, the upper surface 

 ■of which may be either plane or convex. These stones do not figure very largely in the 

 precious stone trade, and are used most extensively in the countries in which they are found, 

 namely, in Russia and North America. Several pounds may be paid for specially pure and 

 fine stones of very intense colour or extraordinary size. The mineral is used not only as a 

 ;gem but also in the manufacture of small objects of various kinds, such as bowls, vases, the 

 stocks of seals, &c. 



SUN-STONE. 



The term sun-stone is applied to felspar of various kinds which have one feature in 

 common, namely, the reflection of a brilliant red metallic glitter from a background which 

 has little transparency and which is pale or almost white in colour. This metallic reflection 

 is specially intense in direct sunlight or in a strong artificial light. The points which 

 reflect the glittering light may be distributed singly and sparingly over the surface of the 

 stone, or they may be numerous and closely aggregated ; in the latter case there is over the 

 whole surface a brilliant and glittering sheen. It is obvious that the name sun-stone is 

 descriptive of this peculiar feature. 



The explanation of the phenomenon is comparatively simple. Enclosed in the substance 

 of the felspar are numerous minute and very thin scales of the mineral haematite (micaceous 



