OR YCTOGN OSY. 
im common life. ‘There are fix varieties of it: wiz. maffive ; 
to the greateft magni n na 
without any particular reas is in {mall pieces, not exceed- 
ing the fize-of a hazel-nut, incorporated with another folid 
e 
mineral ; coarfely diffeminated, implies the fize of a hazel- 
nut a pea; finely di ee 1s from the. fize 
of a o that of a grain of millet; and utely dif- 
eanel cu the fize of a grain of "millet till it is {carcely 
perceptible to the eye :—in angular pieces ; thefe are either 
arp cornered, as in calcedony and quartz, or blunt cornered, 
al :—in grains, which are either loofe or im- 
—in plates ; diftinguifhe 
and into thin plates, as in eeois filver ore ; —in membranes ; 
thefe differ from es pre oe in being ftill cases ft 
mon paper 
2 rticul 
der this denomination exhibit a greater or lefs refemblance 
both to natural and saga obieae sot are gage par- 
he former, they ar ufual or 
filver filiform, or thread-fhaped ; native filver :—capillary, 
culated, or net- 
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dendritic, or tree-fhaped ; native filver and gold : ~eorallaid, 
or branched ; the fhape of corals, asin the beautiful variety 
of arragonite called flos ferri :—{talactic, or ftalactitic ; cal- 
careous finter, brown iron-ftone, calcedony : seactub lorics : 
laviform, or club- “tha ed: i_feuticots, or fhrub-like ; all 
thefe forms are obfervable in calcareous al brown hewias 
fe kd 3 of which 
; “a 1s fubdivided 
into perfe&tly globular, as in 3; elliptical, as in 
quartz and flit ; amygdaloid, as in zeolite; fpheroidal, as 
y3 and imperfedly g 
matite, nitive 
arfenic, and oe :—tuberofe, or lenob-tha ed; as in 
c as in quartz from Schemnitz: (d) imprefed ; of 
shich’ there are fix varieties, viz. cellular ; a is fub- 
with impreffions ; of thefe the cubic, the pide Goan the 
conical, the tabular, and the globular are the moft remark. 
le :—perforated ; as in Sales iron ore; ~corro ea as 
4 quartz, galena, and « :—amorphous ; fares 
with irregular and indeterminable eee, as in {wamp py 
; asin lavas and pumice-ftone : (e) con- 
is variety, wiz. ramote ; ; 
Vaca 
. Regular pita i orms or C' sryflallzzations. — In defcribing 
cry ita hzations we 
onfider 
A. The poo il ‘Quality of the Cryftals, which is either ge- 
a XXV 
nuine or fpurious. Spurious or fio oie cryftals are 
diftinguifhed from genuine or tru eing often 
hollow, having a rough or drufy furfae, and the folid angles 
or edges never fharp or well defined ; examples are pe in 
quartz of the {purious — of the cube and of t 
tahedron of fluor fpar, 
B. cid a Cr yc al. —This is oo of planes ; 
of edges form y the junction of two planes; of plane 
angles; and af folid oo formed by the union nae three or 
more planes in one poin 
To determine the form of cryftals it is neceffary to 
fine the fundamental figures, and then the feveral fede 
fications of thefe forms 
a. The Parts of the fsdenestal Form are :—planes, which 
are either lateral or terminal; edges, which are alfo either 
lateral or terminal; and folid angles, which have been de- | 
fined above 
Varieties of the fundamental Form.—They are the ico- 
fahedron, which is compofed of twenty cuales trian- 
gular planes; asiron pyrites :—the dodecahedron, compofe 
of twelve regular pentagonal planes that meet under obtufe 
angles ; as in iron pyrites and white cobalt : —the hexahe. 
dron, including the cube ad the rhomb, compofed of fix 
quadrilateral planes;  calca {par, fluor fpar:—the 
prifm, confiing of an ape inate number of quadran- 
gular lateral planes, terminated ie aaa o planes parallel to 
each other, and having each a eevee! = as the prifm 
he lateral ‘planes: eka areous {par e pyramid, which 
is compofed of an aeagiinwa ae of triangular, la- 
teral planes, converging to a point, and of a 
as many fides as the figure has lateral planes; quartz, cal- 
careous {par : —the table, which is compofed of two 
d 
n:mber of terminal planes; tabular bar thee — 
= compoled of two convex planes; fparry ir 
Differences in each fundamental Form.—Thefe fu nda- 
bere torms differ from each other 
city, number of planes, fize of the planes, angles u under 
which they meet, direction of the planes, ‘and. fullnefs of 
the cryftal. 
a. Simplicity. —Th confined to the pyramid, 
which is either fimple or aan “The fimple figure is alfo 
diftinguithed in regard of its pofition, which is either ere& 
latter, which adheres by its fummit, is 
double figure the lateral planes of the on 
pyramid are fet either on the lateral edges, or lateral planes 
of the a 
B. ie r of Planes.—The number of planes in the 
iecfahetnn Ga hea hexahedron, and lens, is always 
f determinate 5 but 
i 
(mo e feldom with eight or nine). and t 
pyram mid occurs with three, four, fix, and cok fides ; the 
table has four, fix, or eight terminal planes. 
y+ The Size of the Planes in — to each other —They are 
the latter cafe, either intle- 
the v arieties cb- 
t 
with ‘planes pein broad and narrow ; with t 
fite planes broader ; with two opprfite planes 2 a 
&. Angles under which the Planes meet. —Vhefe a 
of the iaceral edges, of the term er cigs and of the fum. 
mit. Angles of the lateral edges: 
oblique angular, as in rho. : i 
angular, as in topaz. Sale a the terminal edges: thefe are 
4L either 
