MINERALOGY. 6 3 



There is, however, another of the fame 

 kind in Sweden^ which by reflection ap- 

 pears rather brown - y but by refraction is 

 red, with violet veins. 



b. The white opal. Its ground is white, of 

 a glafs-like complexion, from whence 

 are thrown our green, yellow, and bluifri 

 rays; but it is of a reddifh or rather flame 

 colour, when held againft the light, 

 i . Of many colours. Th^ oriental opal. 



2. Of a miiky colour *, from Eibenitock, 

 in Saxony. 



3. Bluilh, and femi-tranfparent. This is 

 not fo much valued, as thofe which are 



* I have lately got afmall piece of pfeudo-agate, from the 

 Eaft-Indies, which is of a yellowifh brown, and pale blue, or 

 rather miiky colour, with a mining brightnefs, exactly like 

 that of the milky opals of this feclion, and received alfo fome 

 other fpecimens found at St. Georgio, near Turin, in 

 Piedmont, there called by the name, Pfcudo agate (Baftard 

 agate), a name which ieems very well adapted to this 

 ftone, fince in every refpecl, hardnefs excepted, it comes 

 neareft to the agates ; becaufe, 1. It is tranfparent in the fame 

 degree as agates, and varied with red and grey colours, inter- 

 fperfed {onetimes with white opaque veins, or rings, and 

 black dendntical figures. 2 It is of a very fine and mining 

 texture, when broke, rather fuperior to that of the agates, but 

 fo foft, that it fcarce yields any fparks, when ftruck againft 

 fteel; and does not admit of any polifh, but what is inferior 

 to the luftre of its natural texture : however, it /lightly marks 

 common window g'afs. 3. When broke through the den- 

 drites, it is as fmooth and mining at that place as in any 

 other ; and thefe dendrites vanim in the fire, without leaving 

 any pores in the ftone. 4. It does not melt before the flame, 

 by the blow-pipe, but becomes perfectly white and opaque. 

 5. Nor is it fufible even with borax. 6. It does not ferment 

 with the acid of nitre. 



So«ne« 



