4 
Mr Brooke on CrystalUsatldn. 
know^ from the copious deposit of siliceous matter from the 
ters of the Geysers in Iceland, and from the hot-springs in the 
island of St Michael’s, that quartz may be held abundantly in 
solution by water. 
Whether the metals have been deposited from chemical solu- 
tions, or from a state of fusion, are points upon which we possess 
no certain information ; nor do the few facts with which we are 
acquainted tend to throw much general light on the subject. 
Some specimens were described by Mr Aikin in the Geolo- 
gical Transactions^ which were brought from Torre del Greco. 
Among these were some minute octahedral crystals of red oxide 
of copper, attached to the surface of a fused, and partly oxi- 
dated, mass of copper and iron. These must have been pro- 
duced by sublimation of the particles which composed them. 
It appears from a paper by Dr Wollaston, published in the 
Philosophical Transactions for 1823, that the metallic titanium 
which he discovered among the slags from some iron-works, is 
wholly infusible ; but he conjectures that it might have been 
precipitated, in its present crystalline form, from a state of 
oxide, in which it might have been sublimed ; and in this man- 
ner crystals of the metals and their ores may possibly have 
been deposited upon quartz or upon other earthy substances. 
The red oxide of mercury produces sometimes very distinct 
crystals by sublimation ; and crystals of calomel and of other 
substances may be produced in a similar manner. 
The processes of the laboratory are the only means we pos- 
sess of investigating the phenomena of crystallisation. The art 
of the chemist has, however, as yet succeeded in imitating the 
composition of very few only of the natural minerals ; and the 
number of these which he has reduced to crystalline forms is still 
less. Some minute crystals of cpiartz are said to have been de- 
posited from an alkaline solution of that substance, after long 
standing ; and crystals of carbonate of lime have been observed 
in vessels which contained the elements of that mineral in solution. 
Lead may be produced in thin metallic plates, from the decom- 
position of acetate of lead by metallic zinc ; and the crystallisation 
of metallic silver will take place in an equally well known chemical 
experiment. Bismuth, antimony, and some other metals, may also 
be made to crystallise by fusion. But these few facts afford no 
