Prof. A. II. Church — Specific Gravity of Precious Stones. 321 



It will be seen from these determinations that the density of this 

 species (beryl) is remarkably constant. I found very nearly 2 - 7 for a 

 crystal of emerald of good colour, but the number would doubtless have 

 been rather higher had there been no flaws in the specimen. 



No. Name. Remarks. Spec. Grav. 



6. Chrysoberyl. Golden yellow, flawless 3-84 



7. ,, Brownish yellow, flawless 3*734 



8. * ,, Yellowish brown, flawless 3-7 



9. * „ Emerald green, slightly flawed 3-86 



The above numbers serve to show that clrrysoberyl may be dis- 

 tinguished from chrysolite by its specific gravity, although the 

 greater hardness of the former species is sufficiently decisive on this 

 point. Jewellers constantly make a confusion between the two 

 stones, especially in small specimens of a yellow hue ; but the follow- 

 ing determination of the specific gravity of a good chrysolite shows 

 this stone to be less dense than the former : 



Peridot of rich green colour, flawless 3*389 



The same stone as No. 10, after ignition 3-378 



Essonite, nearly flawless 3-631 



Essonite, flawed 3-604 



Essonite, slight flaws 3-666 



Essonite, a fine specimen 3-642 



Dark red, flawed and opaque in parts 4-058 



The same stone after heating 4-044 



Eed, transparent 4-059 



The same stone after fusion... 3-596 



Clear red 3-89 



Very pale brownish red ; 3-682 



Eather darker than No. 21 3-696 



Nos. 12 to 15 were specimens of the stone usually called by jewel- 

 lers the jacinth. The above determinations are corroborated by a 

 series of specific gravities of this stone communicated to me by Mr. 

 Rudler. The deep red or precious garnet often has a specific gravity 

 close to that of the ruby. Specimens of a fine variety of red garnet 

 have been lately sold for the true ruby ; indeed, one of these garnets, 

 well cut and mounted with diamonds, requires a practised eye for the 

 recognition of its real character. 



23. * Quartz. ... Milky, banded, flawless 19° 2-642 



24. „ Amber yellow, flawless 2-647 



25. „ Pale brown, with whitish streaks 2-651 



26. ,, Smoky, pale brown 266 



27. ,, Pure rock crystal 2-65 



28. ,, Pale yellowish brown, flawless 2-663 



29. ,, Amethyst, very dark 2-662 



30. „ Amethyst, dark 2-658 



31. „ Amethyst, not so dark as Nos. 29 and 30 2-659 



The above numbers seem to show that dark-coloured amethyst is 

 really denser than pure crystal ; while the latter, again, is denser 

 than milky quartz. 



32. Sapphire. ... A white crystal, banded with blue 3-979 



33. „ Golden yellow, flawless 4-03 



34. „ Yellowish grey, subtranslucent 3-94 



DECADE II. — VOL. II. — NO. VII. 21 



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