RUBY. 
395 
found in a ferruginous volcanic sand, with little 
hyacinths resembling those of Ceylon. <£ There 
are,” says Faujas, “ several sapphires in the ferrugi- 
nous sands of Expailly, mixed with garnets and hya- 
cinths. I am convinced that they are true sapphires, 
and not coloured rock crystals, as several naturalists 
would have us believe.” 
The sapphire is found to vary in colour : it is 
generally of a transparent blue; but M. Engestrom 
found some of a milky colour, which, when looked 
through, varied in the same manner as the milky 
blueish opals. The late king of France had one 
with a yellow stripe of a fine topaz in the middle, 
and some are met with half green and half red. 
The sapphire is the third in hardness, the ruby 
being the hardest of all after the diamond. It be- 
comes electric when rubbed, and is found in Siberia, 
Bohemia, Alsace, and Auvergne. Rome de ITsle 
speaks of one from this last place which was en- 
tirely green or blue, according to the side it was 
looked through. Magellan tells us that sapphires 
are preferable to common rubies for jewelling the 
pallets of escapements, and the holes in wheel- 
pivots, in astronomical watches and clocks, on ac- 
count of the regular hardness of their substance. 
A good sapphire of ten carats is valued at 50 guineas. 
If it weighs 20 carats its value is 200 guineas ; but 
under ten carats its value is estimated at a much 
lower rate. 
The topaz is a precious stone of a pale yellow 
