OF CORNWALL. I2I 
edge, underneath which there is a tendency towards forming another 
equal pyramid ; a tendency compleated in Fig. xiv. where the py- 
ramids are nearly equal, on one fquare bafe common to both. 
The cryftal, Fig. xvi. Ihoots in a triangular form, like a wedge. 
Fig. xvn. is tabular, the planes pentagonal, the Tides quadran- 
gular. 
Fig. xviii. is a draft on a rhombic bafe. 
Fig. xix. conlifts of a pentagonal fhaftj it is pointed, but very 
obtufely, at each end, the cufpides being comprefled almoft into 
one hexagonal plane. It breaks into rhomboids. 
Fig. xx. is the plan of the bale of an hexagonal flattifh piece of 
cry dal Fig. xxi, whole ddes are alternately wide and narrow at its 
top and bottom. Thefe figured crydals, N°. vm. and from xn. to 
N“. xx. are all from theLong-clofe copper-work inCamborn, and being 
heated gradually (for if violently fcorched they will fly) by applying 
a hot poker, or rather placing them in a crucible over a gentle fire, 
will throw forth a lambent flame of the rainbow colours, like a 
native pholphorus. 
Fig. xxii. exhibits a polyhedron of cryflal. 
Fig. xxiii. is the plan of the circular bale of two cylindrical 
columns, Fig. xxiv. of fhotten cryflal, the only one of that form 
which I have feen. 
Fig. xxv. is the bale of the frujlum of a cone ; the exteriour ring 
of cufpides is bright amber; the next plain opake white; the third 
radiated, the rays tending from the centre ; the next opake white, 
till you come to the central nucleus which is an irregular Ipeck of 
the yellow copper ore; Fig. xxvi. is the elevation of this frujlum \ 
Fig. xxvii. exhibits a piece of hexagonal cryftal of the fineft 
water, inclofing green fprigs feemingly of mofs. This happens 
fometimes to cryftal, and doubtlefs to our Cornilh cryftals as well 
as Others \ « A piece of cryftal (fays Dr. Grew, Muf. R. S. Part III. 
Chap, iv.) in which is immerfed a molly fubftance of a reddilh co- 
lour, and there are lome cryftals have been known naturally to 
inclofe a liquor.” 
Fig. xxvm. is a duller of femipellucid cryftal fliot into reclined 
cones, which make an angle of near forty degrees with the 
furface of the ftone. The fides of thefe cones are very curious 
fret-work of little lpires or briftles, many of them fharp as the 
fmalleft needle, and pointing nearly in the fame direction as the 
cone on which they rile. The furface of thefe Ihoots is of a ferru- 
ginous flint-like fubftance, but the infide more clear and tranlpa- 
n Mr. Lhuyd has a fpecimen of like fhape, but 0 This fpecimen was not found in Cornwall, but 
a iparry balls which he calls Fluor triquetrus, is introduced to fhew that cryftals inclofe, and 
. xxxiv. I able i. of his Lithophylacium. therefore have been formed firice plants. 
I i 
rent. 
