308 M. Daubrée on the 
It is besides important to observe that the crystallization 
of these compounds takes place at a temperature much below 
their point of fusion. 
With lime, magnesia, alumina, and glaucina, we obtain 
crystallized quartz under the ordinary form of a pyramidal 
hexagonal prism, and a part of the base passes into the state 
of silicate. 
It isin this that the silicate of lime, named Wollastonite, has 
a great tendency to be produced, in rhomb tables with two 
broad truncated faces which replace the obtuse angles, the 
constant form of the natural crystals. These tables are 
often grouped perpendicularly between each other like the 
prisms of Staurotide. 
It is in this way that, with the magnesia, we obtain peridot 
in rectangular prisms. 
Alumina yields a silicate in elongated prisms with oblique 
bases, not acted upon by acids, and infusible, with all the 
characters of disthene. It is interesting to see in this case 
the chloride of aluminum forming at the expense of the 
silicium. 
In order to form a double or multiple silicate, it is neces- 
sary not only to mix the bases, that they may become silici- 
fied in the suitable proportions, but also to furnish the oxygen 
necessary for the formation of the silicic acid, by adding in 
excess one or other of them, or lime. 
A mixture of lime and magnesia yields crystals of pyroa- 
enous diopside, without colour and of perfect limpidity ; they 
present the large truncation and bevelment common to 
augite. 
Seven equivalents of potassa or soda, one equivalent of 
alumina, or else an equivalent of alumina with six equivalents 
of lime, produce, under the reaction of chloride of silicium, 
crystals of oblique prisms with obtuse bevelments, nearly 
unaltered by sulphuric acid, fusible by the blow-pipe. and in 
short presenting all the characters of the felspars. 
By the same process, and by varying the nature and pro- 
portion of the bases submitted to the chloride of silicium, I 
have obtained silicates with the crystallographic and chemi- — 
eal characters of Willemite, idiocrase, garnet, phenakite, — 
emerald, euclase, and zircon. 
