21 
which, like the chrysoprase, owes it green colour saloon. 
to oxide of nickel—By way of appendix to the N/ f7 hST , 
calcedonic substances, are added a few specimens 
of the less compound varieties of agates, in which 
common calcedony, carnelian, and heliotrope res¬ 
pectively form the predominant ingredients.—Of 
flint, a well known mineral substance, several 
interesting varieties are deposited in this case. 
(Case 8.) Contains principally opaline substan¬ 
ces, viz. specimens of the noble opal, which owes 
its beautiful play of colours to a multiplicity of 
imperceptible fissures in its interior ; the Mexican 
sun or fire opal ; the common opal, a translucent 
white variety of which, appearing yellow or red 
when held between the eye and the light, is cal- 
led girasol; the semi-opal, agreeing in its princi¬ 
pal characters with the common ; specimens of 
those varieties which, having the property of 
becoming transparent when immersed in water, 
are called hydrophanes, and vulgarly oculus mundi; 
wood opal, or opalized wood; jasp-opal, referred 
by some authors to jasper ; the menilite, called 
also liver-opal, found at Menil-Montant, near Paris, 
in a bed of adhesive slate, a specimen of which is 
added. Some varieties of cacholong may likewise 
be referred to the opal-tribe.—The remainder of 
this case is occupied by the siliceous substance called 
hornstone, divided into the conchoidal and splin¬ 
tery varieties ; among these are the remarkable 
pseudomorphous crystals from Schneeberg, in 
Saxony, 
v 7 
