Analyfu of the Spinel. - 349 



VI. 



Analyfu of the Spinel. By Profefor KlAPROTH. * 



HE fpinel appears to me to be among thofe precious ftones which ought to be placed 

 in the clafs of hyacinths of the ancients. For they do not defcribe its colour as being a red 

 inclining to yellow, like the hyacinth of the moderns, but as being of a clear violet, and alfo 

 of a rofe colour. We read, for inftance, in Pliny f, Multum ah amethifio d'tjlat hyacitt' 

 thusy tamen i vicino defctndens. Differentia hac quod tile emicam in amethifio fulgor vio- 

 laceus dilutus efi in hyacintho. Epiphaius reckons five kinds of hyacinths, of which he 

 terms the third yxTtlSog t, and Salmafius defcribes its colour in thefe words, inter rofetm efl 

 et dilutiorem. The modern hyacinth has been confounded with that of the ancients, no 

 doubt, from the following paffage of Pliny §, Hyacinthos Ethiopia mittit et chryfolithos aure» 

 colore tranjlucentei : but this, by a well-founded criticifm, may be read thus, Marcefcem cele- 

 rius nominisfuiflore hyacinthus, Ethiopia mittit et chryfolithos, &c.; in which cafe, the aureus 

 color of the latter, which is known to be the modern topaz, will have no application to the 

 hyacinth, and we flial! have at the fame time one contradi£lion lefs in Pliny. 



The fpinel has hitherto been clafied among the rubies as the fecond fpecies of that 

 genus, the true ruby being the firft. But fince Rome de I'lfle || has fhewn the different 

 cryftallization of thefe two ftones, and has (hewn that the figure of the ruby, of which 

 Pegu is the country, is an elongated double hexahedral pyramid, modern mineralogifts 

 have clafTed it among the fapphires as a red variety, and have confidered the fpinel as a par- 

 ticular genus ; a diftindtion which the differences of hardnefs and fpecific gravity appear alfo 

 to point out. 



In doubtful cafes, the fraflure may determine the fpecies. The fpinel has a foliated frac- 

 ture, the plates being difpofed in three different dircdions ; but the lapphire has a conchoidal 

 frafture on all fides **. 



Chemical analyfis is always the moft decifive. But the fcarcity of the ruby in its natural 

 ftate, cryftallized in the hexahedral pyramid, or the red fapphire, leaves us little reafon to hope 

 for fuccefs in this refpeft. 



The primitive figure of the fpinel is an octahedron, or double tetrahedral pyramid. This 

 cryftallization is rather frequently found in a perfect ftate, but much oftener with fome con* 



* Beitrage fur chemifchen keutnifs, vol. II. 

 •}■ Lib 37, c. 9. 



% From the Arabian word, fignifying the colour of red chalk. See Joan de Laet de Gemmis et Lapid. 

 Lug. Bat. 1647. § Loc. citato. |{ Cryftallographie, I. 113. 



** Mineralogy of Eftncr, II. feft. i, p. 96, 97. • . , 



Vol. III. — November 1799. Za fiderablc 



