317 
m i 
images of the Virgin Mary. Its fpecific gravity varies 
from V65 to 2‘93 : but the analyfes which we poffefs of 
this fubftance vary confiderably with re fp eft to the rela¬ 
tive quantity of the conftituent parts of the feveral varie¬ 
ties. The following are the proportions according to 
Bergman. 
Vauquelin. 
Klaproth. 
Silica 
40 
r- 
50. 
-I 
47. 
_A- 
4 s. 
-i 
42..50 
Argil 
46 
35 - 
20, 
34-*5 
I I.5.O 
Magnefift 
5 
i -35 
-- 
9 - 
Oxyd ot iron 
9 
7.0 
15.50 
4.50 
22, 
Manganefe 
— 
—— . 
1 -75 
0,50 
2. 
Lime 
-.— 
1.33 
-- 1 
--— 
-- 
Potalh 
— 
-—- 
13.50 
8.75 
IO. 
Lofs 
-- 
5.33 
2.25 
4 . 
3 - 
ICO 
IOO 
IOO 
IOO 
IOQ 
s. Mica laminofa, or laminous mica: tranfparent, co¬ 
loured, with large parallel eaiily-feparable plates. Found 
principally in the granites of primeval mountains ; gene¬ 
rally fmoke-colour or black; fometimes brown, gold, red, 
or white; and very rarely concreted in maffes refembling 
pieces of lhale. 
3. Mica fquamofa, or fcaly mica: fomewhat opake, with 
fmaller lcattered incurved foliations. It is fometimes of 
11 filvery colour, and fometimes of a gold colour; and, 
from its lultre, joined with its colour, has occafionally 
been really miftaken for iilver or gold. Miners call this 
cat-gold or cat-Jilver. There is a patch of mica of this 
kind on the ridge of Malvern, between the well-houfe 
and the town. 
White or greenilh mica may be diftinguifhed from talc 
by its elafticity, and by not poflefiing the un&uous feel 
of the latter fubftance ; from felenite, by remaining un¬ 
altered in a low red heat; from fulphuret of molybdena, 
by its elafticity, and by not ftaining paper when rubbed 
upon it; from cryftallized oxyd of uranium, by its elafti¬ 
city, and by not palling into the ftate of a black fcoria 
under the aftion of the blow-pipe; from grey micaceous 
iron ore, by being lefs fragile, and by adhering lefs eafily 
to tire fingers when crumbled; alfo, by not being mag¬ 
netic, as that often is. 
4. Mica undulata, or undulated mica. Of this fpecies 
there are two varieties, a, with undulate gold foliations ; 
g, with flexuoule brittle gold foliations. Both are found 
in the mines of Dalecarlia in Hungary. 
5. Mica haemifpherica, or hemifpherical mica: with he- 
mifpherical concentric foliations. Found in Finland, in 
the hamlet Kimito, conftituting a component part of de¬ 
caying rock ; white, very lhining, and refembling in bulk 
and figure the half of a fplit pea. 
6. Mica ftriata, or ftriated mica: with the foliations 
radiating. Found in Saxony, in ftones; cinereous or 
black, becoming whitifh or yellowilh in the fire, and ap¬ 
proaching near to-a hornblend. 
7. Mica cryftallina, or crylialline mica: in fix-fided ta¬ 
bles. Found in the mines of Dalecarlia, in Salzburg, and 
Zinnwalden; the tables fometimes fcattered, fometimes 
aggregate in a ftellate manner, or difpoled in columns. 
8. Mica prifmatica, or prifmatic mica: brown, in nine- 
fided prifms. Found in the mines of Saxony, near Schnee- 
berg, in rock compofed of quartz and feldfpar; opake, a 
little filming within. 
9. Mica lepidolithus, or lepidolite: with fcattered 
flat, cohering, pale-violet, fcales. This is found in Mo¬ 
ravia and Sudermania, mixed with granite, in large amor¬ 
phous maffes; and is compofed of thin plates, which fe- 
parate eafily. Colour of the mafs violet blue, of the thin 
plates filvery white ; powder white with a pale red tinge. 
Before the blow-pipe it froths, and melts eafily into a 
white femi-tranfparent enamel full of bubbles: diffolves 
borax with effervefcence, and communicates no colour 
to it: effervefces flightly with foda, and melts into a 
mafs fpotted wdth red: with niicrocofniic fait, it gives 
Von. XV. No. 10,4-5. 
C A. 
a pearl-colo'ur globule. Contains file* 53, alumine 20, 
potalh 18, flu'at of lime 5, oxyd of manganefe 3, oxyd 
of iron i. 
10. Mica ardefiata, mica-flate, or micaceous fiiiftus : 
compofed of mica and quartz, difpofed in layers, which 
are more diftindt than thole of gneifs, into which it is 
frequently feen to form a tranlition. The colour of the 
mica, which generally forms the predominant part, is 
ufually of a- grey colour, mixed with greenilh ; the quartz 
is aimolt al ways white. 
This primitive rock, which is of great importance to 
the miner, as being particularly rich in ores, contains 
alio frequently other minerals,,particularly common and 
noble- garnets, which may even be conlidered as forming 
an effential component part of mica-flate; Ihorl, both the 
common and tourmaline, (luch as that of Dunkeld and 
Blair-in-Athol in Scotland;) kyanite, (which has been 
found in the varieties from Mainland, one of the Shet¬ 
land iilands, and near Banchory in Aberdeenlhire;) rutile, 
(that of Salzburg, Hungary, &c.) feldfpar, but only in 
Angle grains. 
Befides the common mica-flate, which is ftraight, and 
rather thick flaty, the Wernerian geognofians diftinguifii 
three other varieties ; viz. the undulated mica-flate, which 
lias not been found to include other fiubftances; the 
talcky mica-flate, which is ftraight flaty, compofed of 
green mica, and traverled by thick layers of quartz; and 
laltly, the fine flaty variety, which forms a tranlition into 
clay-flate, which refts on it; it is generally of a greyilh- 
yellow colour, and almolt entirely unmixed with quartz. 
As mica-flate palles on one fide into clay-ilate, (the next 
rock in lucceifion,) in the fame manner it forms a very 
diltindt tranlition into gneifs, on which it refts ; the out¬ 
goings of its ftrata being low'er than thofe of the latter, 
and higher than thofe of the clay-llate, which ulually 
cover them. It furrounds the older rocks in mantie- 
ihaped ftratification. The mica-flate mountains, which 
are generally much lefs craggy and bold than thole of 
gneifs, contain far more foreign beds than both granite 
and gneifs mountains ; the moft remarkable beds ob- 
ferved in them are thofe of granular limeftone, of horn¬ 
blende flate, hornblende rock, and adlinote ; as likewile 
galena, copper and iron pyrites, magnetic iron-ltone, and 
other ores. The greateft part of the metalliferous mines of 
Sweden and Norway, and feveral of thofe of Hungary and 
Saxony, are fituated in this rock. Mica-flate conllitutes 
conliderable mountains in moft parts of Europe, and alfo, 
according to Humboldt, in South America. In Scotland, 
it occurs abundantly in the valley between Dunkeld and 
Blair-in-Athol, on the mountain of ~Schehallion, in the 
illand of Arran, the illand of Jura and Ilia, &c. It is often 
employed for conftrudting or lining furnaces, whence it 
has been called Gejlellftein, or Saxum fornacum ; names- 
which are, however, given to feveral other fofiil rocks 
applied to the fame purpofe. 
11. Mica micarella, or micarel flate: fo called by Pin¬ 
kerton, who fays it has commonly been confounded with- 
mica-flate, and has the fame general appearance; the 
fpangles having however fometimes more of the Iilver 
lultre, and in other examples more of the undluous calt 
of talc, than is obfervable in mica-flate, where the mag- 
nefia is ltrongly impregnated with iron. It has alfo the 
ul'ual adjundts of talc, and feldom contains garnet, or the. 
other fiderous fubltances’ that are found in mica-flate.. 
In decompolition, it fometimes forms plates or iiiinitions 
of fteatite between plates of quartz. Its longitudinal, 
fracture is fmall-grained and uneven; the crofs-fradture, 
is imperfect and foliated. The fragments are indetermi¬ 
nately angular, fometimes blunt-edged. On the edges it 
is flightly tranlluceftt; it is loft, ealily frangible, and not 
particularly heavy 5 the fpecific gravity, according to Kir- 
wan, is 2’98. < With regard to its chemical character, it 
experiences no alteration before the blow-pipe, either 
alone or with the addition of borax. With carbonate of 
foda it forms an opaque fcoriaceous globule; and with 
4 M iftiqrocoiBiiC 
