Earths. 
pennyweights i8£ grains Troy ; and a fragment of a crys¬ 
tal from the fame trafr of country, now in the pofl'effion 
of Mr. Farquarfon of Invercauld, weighs i pound 3 ounces 
8 drachms and 8| grains Troy. Another topaz has been 
found near Invercauld in AberdeenIhire: its weight, as 
communicated to me by Col. Imrie, is 3420 grains, or 7 
ounces 2 pennyweights 12 grains; its fpecific gravity 
3-56. It is laid, that a diftinbt cryftal, heavier than the 
preceding one, has been found in the fame county, and 
is now in the pofleflion of a gentleman in Aberdeen. The 
nature of the repofitory of thefe topazes has not, it fliould 
feem, been alcertained; but the author of this paper con- 
jeftures, and on very plauiible grounds, that they may 
occur in drufy cavities, or veins, in granite, and in con- 
fiderable quantity. 
Great numbers of topazes have been lately brought to 
this country from Botany Bay. Mr. Mawe has parcels of 
them, which have exactly the characters of the topaz of 
Scotland. As this fall is much fcarcer and dearer than 
the Botany-Bay topaz, there is reafon to fear that the 
latter may be fubftituted for the former. 
4. Gemma hyacinthus, the hyacinth : hard, lamellar, 
of a peculiar yellowilh-red, in four-fided prifms termi¬ 
nated on both fides by a four-fided pyramid ; not fulible 
per fe, but lofing its colour in a ltrong heat. Found in 
the Eaft and in Bohemia, in the form of pebbles, in ob- 
tule-angular pieces. Colour yellowilh-red with a mix¬ 
ture of brown ; the cryftals are lfnall,with afmooth furface 
and foliated texture ; they are imitated by heating rock- 
cryftal and putting it into a folution of dragon’s blood. 
5. Gemma alabandica, the role-ruby : hard, pellucid, 
of a red colour, not fulible, but lofing its colour in a ltrong 
heat. Found in the river Goetch near Lengefeld, in 
Wurtzburg, in the form of rounded granulations, from 
the fize of a pea to that of a bean : when expoled in a 
ltrong heat furrounded with wood-alhes, lofes all its co¬ 
lour, and is often fold for the diamond. 
6. Gemma rubicellus, the occidental or Brafilian ruby: 
hard, of a reddilh colour verging to pale yellow, not fuli¬ 
ble, but lofing its colour in a ltrong heat. Found in 
South America: it is fofter than the oriental ruby, and 
of a much inferior colour ; fraCture foliated. 
7. Gemma fpinellus, balafs or fpinell ruby : hard, of a 
pale red colour inclining to orange 5 not fufible, but lofing 
its colour in a ltrong heat. The balafs-ruby is fo called 
from the word halacckan , the Perfian name of Pegu. In 
liardnefs it is inferior to the oriental ruby. Specific gra¬ 
vity, 3‘6 ; primitive form, a regular oCtohedron: this is 
all'o the form in which it is commonly met with. It is 
laid by Vauquelin to contain, alumine 82147, magnefia 
8-78, acid of chrome 6‘i8. Cryftals and fragments of the 
fpinell-ruby conftitute more than nine-tenths of what is 
known in commerce by the name of fund of Ceylon. This 
land is a collection of various precious itones feparated 
from the lediment of the rivers of that illand, by which 
they have been conveyed from the interior: but, as a fe- 
leftion of the molt valuable has already been made in In¬ 
dia, where they receive their fir ft polilh, cryftals of the fpi¬ 
nell of any remarkable fize or beauty are rarely met with 
In the fand when it is imported into Europe. The fpinell 
is met with in the fame fituation with the oriental ruby, 
and principally in Pegu and Ceylon. It is fometimes of 
a yellow and fometimes of a bluifti colour3 fometimes en¬ 
tirely colourlefs. 
8 . Gemma aquamarina, or aqua-marine ; hard, pellucid, 
lamellar, pale lea-green 3 not fufible per fe, breaking into 
trapezoidal fragments. Found in Brafil, India, Siberia, 
Saxony, and Bohemia, fometime amorphous, fometimes 
cryftallized in equiangular fix-fided prifms longitudinally 
ftriated ; its longitudinal frafture rather conchoidal, its 
tranfverfe frafture foliated. It decrepitates when heated, 
and is generally a little difcoloured, but does not melt; 
becomes eleCtric by friftion, when one of its ends is at¬ 
tractive, the other repulfive. Specific gravity, 3-5 5 con- 
459 
tains filex 69, alumine 13, glucine 16, oxyd of iron 1, 
lime 5. 
9. Gemma euclafius, or euclafe: hard, pellucid, lamel¬ 
lar^ green, in four-fided oblique prifms whofe edges arc 
varioufiy truncate and whofe faces are oblique. This 
fubftance has been fo denominated by M. Haiiy, in con- 
fequence of its remarkable fragility. It has the double 
refrafting power to a very great degree. By the blow¬ 
pipe it loles its tranfparency ; and is afterwards filled into 
a white enamel. Specific gravity, 3-06. Contains filex 36, 
alumine 19, glucine 15, oxyd of iron 3. Of all minerals 
this is molt eafily divifible into laminae. There is only 
one known variety in the form of the cryftal of this fub¬ 
ftance ; and this is very remarkable on account of the 
number of its fides ; which, when the variety is perfect:, 
amount to feventy-eigbt. It confifts of a prifm having 
fourteen tides, terminated at each extremity by a fummit 
or pyramid of thirty-two fides. Found in Peru. 
10. Gemma fcorlites, or ihorlite: hardilh, Ibmewhat 
ponderous, diaphanous, of a greenifh or yellowilh-white 
colour, which is not altered by the fire ; not fufible per fe. 
Found in Brafil and in Saxony, with mica or quartz, ge¬ 
nerally in oblong maffes, which when regular are fix-fided 
prifms; frafture uneven, and i'eemingly fomewhat foli¬ 
ated. Specific gravity, 3-53. Contains equal quantities 
of alumine and filex. 
11. Gemma beryllus, the beryl: hard; of a blue-green 
colour, not altering its colour or fulible by heat; of a 
conchaceous texture, which is foliated when broken tranf- 
verfely, in fix-fided prifms, which are ufually longitudi ¬ 
nally Itriate. Found in the mountains of Saxony, Siberia, 
&c. in quartz, granite, wolfram, and other matrices. Its. 
cryftals are of various magnitude, fometimes diaphanous, 
fometimes pellucid, rarely folitary or in pairs, generally 
aggregate or falcicled; colour approaching to green or 
blue, rarely to yellow. Specific gravity, from 2-25 to 278. 
12. Gemma chryfoberyllus, the chrylbberyl : hard, pel¬ 
lucid, green, highly lhining internally, of a conchaceous. 
texture. Found in Brafil and Ceylon, in round mafl'es 
about the fize of a pea, or cryftallized; the form of its 
cryftals being a four-fided reftangular prifin, the molt 
common variety of which is an eight-fided prifm termi¬ 
nated by fix-fided fummits. Colour yellowifn-green^ 
with a fparkling furface. Texture foliated, with the foli¬ 
ations parallel to the faces of the prifm. Caufes double 
refrablion ; is infuiible by the blowpipe. Specific gravity, 
3-698 to 3-761. Contains alumine 71-5, filex 18, lime 6 , 
oxyd of iron 1-5. 
13. Gemma chryfolithus, the chryfolite: hardifh, pel¬ 
lucid, lightifh; of a green colour which vaniihes in a 
ftrong heat 5 fufible by the blowpipe, and fparkling when 
melted ; of a conchoidal texture. Found in Brafil, Cey¬ 
lon, Siberia, Tranfyl vania, and Bohemia ; in angular 
fragments, grains, and cryftallized. Colour yellowilh- 
green mixed with brown, or verging to olive-green. Sur¬ 
face of a fine fplintery or fcaly appearance ; but fuch of 
the cryftals as have not been injured by friftion have 
their broadeft fides longitudinally ftriate ; and, where the 
furface has not fuffered by attrition, it has a confiderable 
luftre; the regular fliape of its cryftals is a fix-fided flat¬ 
tened prifm, terminated in fix-fided pyramids 3 and differs 
from rock-cryftal in having the pyramids more obtufe. 
Specific gravity, 3-4. Contains magnefia 43, filex 38, 
oxyd of iron 19. 
The chryfolite of the moderns, the leaft hard of thole 
ftones called gems, being commonly of fome fhade of green, 
differs therefore, judging by its name, from the chryfo¬ 
lite of the ancients. That probably was either a deepu 
coloured variety of the oriental topaz, or the gem which 
we cal] the hyacinth. The native fituation of the chryfo¬ 
lite is not alcertained. The chryfblites of commerce are 
principally imported from the Levant. They appear Ge¬ 
nerally in the form of irregularly-worn fragments, with 
occafional traces of a quadrangular prifmatic crystalliza¬ 
tion. 
MINERALOG Y. Earths. 
