220 On the Mzcrosco;pical Structure [^ouSSfi?iff 
VI. On the Microscojoical Structure of some Precious Stones, 
By H. C. SoRBY, F.K.S., &c. 
Plate X.* 
A PAPER by myself and Mr. P. J. Butler was read at the Koyal 
Society on February 18tb, in wbicb we described the structure of 
rubies, sapphires, diamonds, and some other precious stones. I shall 
now give a general outline of the whole subject, including various 
facts subsequently learned or scarcely suitable for that occasion. 
It is so very convenient to be able to prepare the specimens 
without having recourse to a lapidary, that it will probably be 
useful to describe how the specimens may be ground to a proper 
form and thickness and the surfaces polished. I shaU confine 
myself to this ; for I have never cut them with a slitting wheel, 
since I can at any time have that operation performed for me under 
my own superintendence; and in many cases specimens may be 
selected of such a form and size that it is quite unnecessary. I 
usually employ a flat plate of moderately stout sheet zinc, which 
does not rust like iron, and has none of the injurious or poisonous 
properties of copper or lead. If it be requisite to grind away much 
from the specimen, and if it be sufficiently strong, I first use the 
finest grain-emery and water, and afterwards the finest washed 
flour-emery. This cuts well without breaking up flawed crystals. 
It should be so fine and free from gritty particles that it produces 
a very smooth surface on such soft gems as garnets, and an imper- 
fect polish on harder minerals, like zircons and rubies. The minute 
scratches should be removed and the surface polished by means of a 
EXPLANATION OF THE PLATE. 
Fig. 1. — Fluid-eavity in sapphire (mag:. 20 linear), with large spherical vacuity. 
„ 2. — „ „ showing the appearance when boiling violently 
as it cools ; mag. 20 lin. 
„ 3. — Fluid-cavity in sapphire, partially divided by projecting plates ; mag. 
50 lin. 
„ 4. — Fluid-cavity in sapphire, of irregular form ; mag. 50 lin. 
„ 5. — Crystals enclosed in ruby; mag. 50 lin. 
„ 6. — Fluid-cavity in aquamarina, with two fluids and a v^acuity ; mag. 150 lin. 
„ 7. — Curious cavity in spinel, with crystals and fluid; mag. 100 lin. 
„ 8. — Fluid-cavity in emerald, with soluble crystals ; mag. 200 lin. 
„ 9. — Crystal enclosed in diamond, surrounded by a cross when seen with 
polarized light ; mag. 1 00 lin. 
„ 10. — Crystal enclosed in diamond, with associated crack ; mag. 100 lin. 
„ 11.— Crystal enclosed in ruby, surrounded by a cross when seen with polarized 
light ; mag. 75 lin. 
„ 12 & 13. — Crystals in spinel, surrounded by cracks mag, 50 lin. 
* The accompanying Plate has been printed from the stone used to print the 
plate in the Proceedings of the Koyal Society, which has been most courteously 
lent for the purpose by Dr. Sharpey, Sec. E. S.— Ed. ^l. M. J. 
