458 
that the hornblende became as diftinCtly cryftallized as in 
the natural fubftance ; fometimes even more fo. And he 
alcertained many very important points as to the nature 
and procels of that cryftallization which took place in this 
mineral fubftance during its confolidation from igneous 
fufion. 
3. Wkin-ftone. Thofe, who do not apply this term as a 
fynonyme with bafalt in general, (fee p. 456.) reftriCl it 
to a variety of this particular fpecies, of a blue or greyilh 
black colour, and rather hard ; found in detached frag¬ 
ments, or forming dykes in mines. It is very plentiful 
in Scotland. 
Order V. SILICEOUS EARTHS. 
Confifting principally of filex, filica, or the matter of 
flint; hard. This order includes the diamond and all 
other precious ftones, befides the newly-difcovered earths, 
and land, &c. Sec. and the moft important and leading 
genus is Gemma, the fpecies of which are the ruby, fap- 
phire, emerald, topaz, See. 
Gemma.— Confining of filex and a larger proportion of 
alumine, with fometimes a little carbonat of lime and 
oxyd of iron : meagre to the touch, of a high internal 
lultre, very rarely opake, breaking into indeterminate 
fragments, parafitical, Alining in the dark, attracting 
light bodies when heated by friCtion ; not melting with 
alkalies. 
1. Gemma rubinus, or true oriental ruby: very hard, 
ponderous, red, of a foliated texture, which in a contrary 
direction is conchoidal; not melting or lofirng its colour 
in the fire. 
The ruby, in its moft perfeCl ftate, is a gem of very 
great beauty and value. It is often found perfectly pure, 
and free from all fpots or blemilhes ; but it is much more 
frequently debafed by them ; and greatly brought down 
in its value, efpecially in the larger fpecimens. It is of 
very great hardnefs, equal to that of the fapphire, and 
fecond only to the diamond. It is various in fize, but is 
lefs fubjeCt to variations in its fhape than moft of the 
other gems. It is moft frequently found very fmall; its 
common fize being that of the heads of the larger fort of 
pins ; and, when of this fize, it is very cheap ; but it is 
alio found of four, fix, or ten, carats 5 and fometimes, 
though but very rarely, up to twenty, thirty, or forty; 
nay, we have accounts of fome of more than a hundred. 
Frutiere affures us very pofitively, that there have been 
rubies in France of two hundred and forty carats. Ta¬ 
vernier tells us he faw one in the Indies of fifty carats, 
which he had a mind to have bought. He adds, that the 
king of France has finer and larger rubies than any in 
the‘poflefiion of the great Mogul. The largeft ruby that 
is known to be in the world was brought from China to 
prince Gargarin, governor of Siberia; it came afterwards 
into the hands of prince Mentchikof, and is at prefent 
one of the ornaments of the imperial crown of Ruflia. 
The ruby is never found of an angular or cryftalline form 
or fliape,but always of a pebble-like figure, often roundifti, 
fometimes oblong, and much larger at one end than the 
other, and in lome forts refembling a pear, and is ufually 
more or lefs flattened on one fide. It is commonly fo 
naturally bright and pure on the furface as to need no 
polifliing; and hence it is worn in rings, and in the 
crowns of princes, in its rough or native ftate. Its colour 
is red in very different degrees, from the deepeft garnet- 
colour to that of the palelt red diamond ; but it ever has 
with the red more or lefs of a purplifh tinge. This is 
very plainly diftinguifhed in the deeper-coloured fpeci¬ 
mens, but in the pale ones is gradually lefs and lefs to 
be diftinguifhed in proportion to their degree of colour. 
Thefe are the diftinguifhing characters of the ruby; and 
by thefe it is eafily known from the garnet, carbuncle, 
and other red gems. Specific gravity, 4'283. 
There are but two places in the Eaft where the true 
ruby is found; the kingdom of Pegu, and the ifle of Cey- 
jon. The mine of Pegu, where it is found in greateit 
Earths. 
plenty, is in the mountain Capelan, twelve days’journey 
from Siren, the refidence of the king of that country. 
The fineft rubies brought hence do not exceed three or 
four carats; the king referving all the larger to himfelf. 
In Ceylon the rubies are found in a river which defeends 
from the mountains towards the middle of the ifland: 
fome few are alfo found in the ground. The rubies of 
Ceylon are ufually brighter and more beautiful than thofe 
of Pegu, but they are rare; the king of Ceylon prohi¬ 
biting his people to gather them, or traffic with them. 
There are, as fome fay, rubies alfo found in Europe, par¬ 
ticularly in Bohemia and Hungary, efpecially the former, 
in which is a mine of flints of divers iizes; which, upon 
breaking, are fometimes found to contain rubies, pre¬ 
tended to be as fine and hard as any of the eaftern 
ones. 
The Greeks called the ruby u-ttvputoi;, “ refilling fire.” 
The ancients, out of their credulity and fuperllition, 
attributed many virtues to the ruby; as that it expels 
poifons, cures the plague, abates luxury and inconti¬ 
nence, banifhes forrow, See. The ruby is formed in a 
ftony fubftance, or bed, of a rofe-colour, called mother of 
ruby; it has not all its colour and luftre at once, but 
comes to it by degrees. At firft it is whitifh; and, as it 
approaches to maturity, becomes red. Hence we have 
white rubies, others half-white, half-red, and others blue 
and red, called lapphire-rubies. When a ruby exceeds 
twenty carats, it may be called a carbuncle; the name of 
an imaginary ftone, of which the ancients and moderns 
have given us fo many deferiptions. There are feveral 
modes of counterfeiting rubies; and fome have carried 
the imitation to that length, that the moft able lapida¬ 
ries, till they come to try the hardnefs, are fometimes 
deceived. See the article Gem, vol. viii. p. 293-298. and 
Glass, p. 602, 3, of the fame volume. 
2. Gemma fapphirus, the fapphire: very hard, fome- 
what ponderous, blue, making a white ftreak, of a flightly- 
incurved lamellar texture; not fufible, but lofing its 
colour in a ftrong heat. Found in Brafil, the Indies, 
Perfia, Bohemia, and near Puys in Velay, fometimes cryf- 
tallized, fometimes in rounded mafles, the angles being 
worn off by friClion; and is next in value to the ruby. 
Colour Iky-blue, or the fliades of Pruflian and indigo 
blue, with fometimes white fpecks. The cryftals are 
ftrong, Alining, and exhibit a foliated texture tranfverfeiy 
ftriate; they become colourlefs when heated with micro- 
cofmic fait, and emit a great light while burning.^ Spe¬ 
cific gravity,. 4. 
3. Gemma topazius, the topaz : hard, ponderous, yel¬ 
low, of a foliated texture which is conchoidal when 
broken tranfverfeiy, not fufible per fe, but lofing all its 
colour in a ftrong heat. Found in India, Brafil, Rufiia, 
Saxony, Bohemia, Sec. generally adhering to other fub- 
ftances, though fometimes detached with the angles worn 
off. Colour a lighter or deeper yellow, moft commonly 
honey-colour, fometimes verging to white or greenifh. 
Its fragments are fometimes irregular, fometimes granu¬ 
lar or prifmatic : the prifms longitudinally ftriate, folitary, 
in pairs, or in threes, difpofed in a cruciate manner ; of¬ 
ten cluttered, rarely four-tided, rectangular, or obliquan- 
gular; more frequently unequally eight-fided, terminated 
by an irregular four or eight fided pyramid, or ending in 
a point. It is infufible per fe, but melts with borax and 
microcofmic fait into a clear glafs. Specific gravity, 3-5. 
In the firft volume of the Memoirs of the Wernerian 
Society, 1811, we have a paper “On the Topaz of Scot¬ 
land,” by Profefl'or Jamelon. According to the profeffor, 
precious beryll, amethyft, precious garnet, and topaz, are 
the only true gems which have been hitherto difeovered 
in North Britain; and the Scottifh topaz was long miftaken 
for a variety of fapphire, till its characters were of late 
fully exhibited in a feries of cryftals, of remarkable fize, 
brought from the upper part of Aberdeenfliire to Edin¬ 
burgh. They are of a greenifh-white hue, and flightly 
opalefcent. The largeft entire cryftal weighs 7 ounces 3 
2 pennyweights,, 
Earths. MINERALOGY. 
