QUARTZ (JASPER) 499 



is found in veins of an inch in thickness in the nickel ores which occur there in serpentine. 

 It is of a dark apple-green colour, and fine plates measuring some square inches in area can 

 easily be obtained. 



JASPEK. 



Jasper is a very impure variety of massive quartz, which is distinguished from hornstone 

 by its large even conchoidal fracture, the dull lustre of the fractured surface, and by its 

 perfect opacity and deep colour. There is no sharp distinction, however, between jasper 

 and hornstone, nor is jasper definitely marked off from other impure varieties of massive 

 quartz, such, for example, as ferruginous quartz (EisenJciesel) . Each of the compact 

 varieties of quartz consists of an aggregate of microscopically small quartz grains ; the 

 superficial characters of each depend upon the precise nature and amount of the impurities 

 present. There are thus no hard and fast distinctions between these varieties ; one 

 specimen will approach more nearly to the character of typical jasper perhaps, and another 

 to typical hornstone, while one end of a third specimen will show the characters of one 

 variety and the other end of another variety, the middle portion being intermediate 

 between the two. In the same way, there is no sharp line of demarcation between jasper 

 and chalcedony, the next variety of quartz to be considered, and there is every possible 

 gradation between typical jasper and typical chalcedony, so that it is sometimes difficult to 

 decide whether a particular specimen should be classed as one or the other. By lapidaries 

 a stone which is perfectly opaque in the sharpest of splinters is referred to as jasper, and 

 one which is slightly translucent as chalcedony. Mineralogically there is no essential 

 difference between chalcedony on the one hand and jasper and hornstone on the other, as 

 we shall see later. 



It has been stated already that jasper is a very impure variety of quartz, containing as 

 much as 20 per cent, of foreign matter or even more. This consists for the most part of 

 clay and iron oxide, these substances in a more or less finely divided condition being 

 disseminated throughout the quartz substance. Organic matter of various kinds has also 

 been observed. It is the presence of such impurities in large amount which conditions the 

 characters of typical jasper, namely, opacity, a large-conchoidal smooth fracture, a dull 

 fractured surface, and a deep colour. A reduction in the amount of impurity present is 

 attended by a lighter colour, a more uneven and splintery fracture, and some degree of 

 translucency in the stone, which thus becomes more akin to hornstone. 



The uses to which jasper is applied depend mainly upon its colour, which, in its turn, 

 depends upon the amount of iron present. A stone which contains but little iron is 

 practically colourless, but shows the other characters of jasper owing to the presence of 

 clay. A white jasper of this description having the appearance of ivory is stated to occur 

 as a great rarity in the Levant and to furnish beautiful gems. The colouring of coloured 

 stones is seldom quite uniform, the different colours or shades of colour exhibited by the 

 same specimen may be in irregular streaks and patches or arranged regularly in parallel or 

 concentric alternating bands. Some stones are traversed by straight crevices and fissures 

 filled with quartz of another colour and sometimes of quite different character. 



The colours most commonly seen in jasper are brown, yellow, and red, green is fairly 

 common, but blue and black more rare. Several colour- varieties of jasper are recognised 

 some of which are distinguished by special names and will be dealt with in detail later on. 



There is considerable variety in the manner in which jasper occurs in nature. It may 

 occur in beds inters tratified with other rocks, or in irregular nodules in various ore 



