Notes on “ Inclusions” in Gems, &c. By Isaae Lea. 201 
taining fluid. In some cases the fluid may be seen to move by the 
unaided eye. In these Herkimer crystals, carbon in the form of 
anthracite is of very common occurrence, and in one of my speci- 
mens a small portion moves in the fluid of a cavity. These cavities 
often exist in an entire sheet, almost across the prism of a crystal. * 
In smoky quartz these cavities are much rarer, as also in 
~ amethyst and wine-colour and green quartz. The amethyst is 
frequently penetrated with crystals of rutile, and these are often 
very large, sometimes one to four inches long. The Chester 
County specimens usually have numerous curved filamentous crys- 
tals, easily detected with a common lens. In Way’s Feldspar 
Quarry, near Dixon’s, Delaware, there is a very peculiar form of 
quartz, which is nearly transparent, but somewhat clouded. The 
fragments of all sizes, from that of a pin’s head to that of a small 
walnut, are enclosed in a mass of Deweylite. These fractured 
pieces are of indefinite forms. They are evidently cryptocrystal- 
line, and look as if they may have been heated and suddenly 
cooled, and thus fractured. When these pieces are subjected to a 
high power, there may be detected in them very minute oval 
cavities in great numbers, and the major axes usually placed in one 
direction I have never seen cavities in milky quartz or blue 
quartz. Sir David Brewster found many cavities in rock crystal 
from Quebec with “ water and mineral oil.” t 
Topaz.—tIn the various beautiful crystals which this mineral 
presents, there are frequently found cavities with fluid, and some- 
times in this fluid may be seen the cuboid crystals described by 
Sir David Brewster. He found a single fiuid in some cavities, and 
in others two fluids with “air-bubbles.” He says the fluid does not 
expand with heat. The Saxony transparent white crystals some- 
times have cavities, as well as those of pale wine-colour. The Bra- 
zilian gold-yellow specimens have these cavities very frequently. 
The clear pinkish are more free from them. I have never observed 
any microscopic acicular crystals in topaz. 
Emerald, Aquamarine, and Beryl—constitutionally the same— 
differ very much in regard to their possession of cavities and their 
commercial value. So far as I have been able to examine fine 
specimens of emerald, it is rare to see one without cavities. One 
which I have, of very fine colour, has many cavities of various 
forms, in which are included a fluid enveloping generally two per- 
fect cubic crystals of an unknown mineral. In all cases in this 
specimen, the second crystal is much the smaller. 
In aquamarine, cavities are not frequent, and in beryl I have 
* Sorby, ‘Journ. Geol. Soc.’ 1858, found many cavities, and thinks that the 
cubic crystals enclosed are probably chloride of sodium, as mentioned above. 
+ The smoky quartz of Pike’s Peak has hexagonal spangles, which may be 
mica. 
t ‘ Trans. Roy. Soc. Edin.’ vol. x. 
