OCCURRENCE OF QUARTZ IN CEYLON. 175 



earth movements, and follow lines of thrust and faulting. The basic 

 lenticles and pinched bands with associated quartz segregations, in my 

 experience, only occur in regions affected by earth movements, and 

 may result from later metamorphism rather than original magmatic 

 segregation. In some cases the veins resemble pegmatite intrusions. 

 The quartz weathers out in small fragments, which may be opaque 

 or transparent. 



Quartz of all varieties in more pr less rounded shapes naturally 

 forms the bulk of the river gravels. Granular quartz pebbles 

 are most common, and transparent cleaved quartz can with 

 some certainty be referred to the same rock which has been 

 subjected to dynamo-metamorphism. The transparent crystals in 

 the river gravels sometimes attain a considerable size, and may be 

 colourless, yellow, or browTi. Such crystals are occasionally sold in 

 the Ratnapura District to Chinese merchants, and fetch a rupee or 

 seventy-five cents a pound. The coloured varieties are also cut as 

 gems, when the stone may be described as citrine or cairngorm, 

 good specimens of which when well cut show a beautiful transparency 

 and depth of colour. 



Crystals of amethystine quartz are often found when gemming. 

 The colour, which is due to traces of manganese, is not, as a rule, 

 evenly distributed throughout the crystal, but confined to the central 

 portion. Hence almost all cut gems of Ceylon amethyst are parti- 

 coloured, but on account of their fine deep purple are highly esteemed, 

 indeed the only other important locality for amethyst is Brazil, since 

 the supply at Oberstein is exhausted. Brazil crystal of all colours 

 is, however, cut at Oberstein. 



Clear quartz containing needles of rutile or tourmaline is known as 

 sagenitic quartz. It is sometimes found in gravels, and may be cut 

 en cabochon to form ornaments that are more curious than beautiful. 



Mention should be made of the quartz cat's-eye or '' tiger's-eye," 

 which contains numbers of minute fibres of asbestos or siliceous 

 pseudomorphs after that mineral, showing when cut en cabochon a 

 ray of light similar, though inferior, to that of the true cat's-eye, 

 which is a variety of chry so beryl. Ceylon is referred to in text books 

 as a locality for the stone, and examples may sometimes be seen in 

 local jewellers' shops. I have however never seen it in the field. 



Recent sandstones and pits of quartz grains with quartz cement 

 occur near the sea coast at Puttalam, Negombo, and other places. 



Coming now to the cryptocrystalline varieties of quartz , excellent 

 examples of chalcedony are sometimes found in the river gravels, 

 doubtless washed from the cavities in decomposed gneiss where they 

 were formed. It also occurs, but rarely, as a thin coating on the 

 joint faces of rocks (Nildandahena). 



Of special interest with relation to stone implements arc the cherts. 

 Chert is an impure siliceous rock containing chalcedony and some- 

 times opaline silica stained with iron oxides. As a rule, the silica of 



