204 
MINERALOGY. 
'-vh'it difficultly frangible, and approaching to 
heavy. It oceans in iron-stone veins, and is 
fr.*« :_iic l in Saxony, and, according to Karsten, 
at ca'i'toi. 1 1 renders the iron ore, along 
tvuii which it is dug, very difficult of fusion. 
1 wenty-sicon j Species. Quartz. 
Y erner divides this into five sub-species, 
amethyst, rock chrvstal (fig. \ r> ), milk-quartz, 
comriion quai tz, and prase. The first sub- 
species is again subdivided into common 
amethyst and thick fibrous amethyst. See 
Quartz, Amethyst, &c. 
Twenty-third Species. Horn Stone. 
_ Horn-stone is divided into three sub-spe- 
cies, splintery horn-stone, conchoidal horn- 
stone, and wood-stone. 
First Sub-species. Splintery Horn-Stone. 
I he common colour grey, but often red, 
with various shades of each. It is usually 
found massive, or in large balls. Internally 
its lustre is^dull ; but glimmering when it ap- 
proaches to the nature of quartz. It is more 
or Jess translucent on the edges, hard, brit- 
tle, very difficultly frangible, and not parti- 
cularly neavy. 
1 he substance is infusible without addi- 
tion; and is found in the shape of balls in 
limestone, and sometimes forming the basis 
ot porphyry. It is a native of Bavaria, Swe- 
den, and tire Shetland islands ; and appears 
to differ from quartz in containing a larger 
proportion of alumina. 
Second Sub-species. Conchoidal Horn-Stone. 
The colour runs from greyish -white to 
yellowish and greenish-white. It occurs 
massive. Internally, it is a little glistening, 
strongly translucent on the edges, hard, 
easily frangible, and not particularly heavy. 
Conchoidal horn-stone is found in beds or 
in veins, accompanied with agate, at Gold- 
berg, in Saxony. 
Third Sub-species. Wood-Stone. 
The prevailing colour is ash-grey, but with 
many different shades. Its shape is exactly 
conformable to its former woody form, whe- 
ther trunk, branches, or roots. Internally, it 
is sometimes dull, and sometimes glimmering 
and glistening ; slightly translucent on the 
edges, pretty hard, easily frangible, and not 
particularly heavy. 
It is found insulated in sandy loam in Sax- 
ony, Bohemia, Russia, Hungary, and at Loch 
Neagh in Ireland. It receives a good po- 
lish, and is applied to the same purposes as 
agate. 
Twenty-fourth Species. Flint. 
The general colour is grey, but with many 
■varieties. It occurs massive, in regular 
plates, in angular grains and species, in glo- 
bular and elliptical rolled pieces, in the form 
of sand, and tuberose and perforated. Some- 
times it is chrystallized, when it exhibits 
double six-sided prisms, or flat double three- 
sided pyramids. Internally, the lustre is 
glimmering, translucent on the edges, hard, 
easily frangible, and not particularly heavy. 
Twenty-fifth Sp ades. C/udcedony. 
This is divided nto two sub-species, chal 
cedony and carnelian. 
First Sub-species. Common Chalcedony - . 
The most common colour is grey. The 
external shape is various, being massive, in 
blunt-edged grains and rolled pieces, in origi- 
nal round bulls, &c. &c. Internally, the chal- 
cedony is almost always dull, commonly se- 
mitransparent, hard, brittle, rather difficultly 
frangible 1 , and not particularly heavy, it oc- 
curs in amygdaloid, and in porphyry ; and 
is found in Transylvania, in Iceland, Siberia, 
Cornwall, Scotland, and the Hebrides. Be- 
ing susceptible of a line polish, it is employed 
as an article of jewellery. 
[Second Sub-species. Carnelian. 
The principal colour is a blood-red, of all 
degrees of intensity. It commonly occurs 
in roundish pieces, and also in layers: t he 
lustre is glistening, bordering on glimmering, 
and is semitransparent. See Carnelian. 
Agate. 
The fossils known under this name are all 
compound substances; and hence cannot 
have a particular place in any systematic ar- 
rangement. Werner therefore has placed 
them as a supplement to the species chalce- 
dony, which forms a principal constituent 
part of them, and disposes them according 
to their colour-delineations, thus: 1. Forti- 
fication agate ; 2. Landscape agate ; 3. Rib- 
bon agate ; 4. Moss agate ; 5. Tube agate ; 
6. Clouded agate; 7. Land agate; 8. Star 
agate ; 9. Fragment agate; 10. Punctated 
agate; 11. Petrifaction agate; 12. Coal 
agate ; 13. Jasper agate. They are all com- 
pounded of chalcedony, carnelian, jasper, 
horn-stone, quartz, heliotrope, amethyst, 
indurated lithomarge, and opal, in different 
quantities and proportions ; and are found in 
great abundance in Germany, France, Eng- 
land, Scotland, Ireland, and the East Indies. 
The uses of agate are various. It is cut 
into vases, mortars, snuff-boxes, seals, han- 
dles to kryves, and for many other useful pur- 
poses. See Agate. 
Twenty-sixth Species. Heliotrope. 
The principal colour is intermediate be- 
tween leek and dark celadon green, or moun- 
tain green. It occurs massive, and in an- 
gular as well as rolled pieces. Internally the 
lustre is glistening, and is always resinous. 
It is commonly translucent in the edges; is 
easily frangible, hard, and not particularly 
heavy. 
Heliotrope is found in rocks belonging to 
the floetz trap formation, in Asia, Persia, Si- 
beria, Saxony, and Iceland. 
On account of its beautiful colour and its 
hardness, it is employed for nearly the same 
purposes as agate. See FIeliotrope. 
Twenty-seventh Species. Plasma. 
Tiie usual colour is intermediate between 
grass and leek-green, and of different de- 
grees of intensity. It occurs, in indetermi- 
nably angular pieces, which have a rough 
earthy crust. Internally its lustre is glisten- 
ing. It is intermediate between semitranspa- 
rent and strongly translucent, hard, brittle, 
frangible without great difficulty, and not 
particularly heavy. 
Hitherto it has only been found among the 
ruins of Rome, and constituted a part of the 
ornamental dress of the undent Romans. 
Twenty-eighth Species. Chrysopras, 
Its characteristic colour is apple-green, of' 
all degrees of intensity. It is found massive 
in angular pieces, and in thick plates. In- 
ternally it is dull; the lustre intermediate 
between translucent and semitransparent. It 
is hard, not very difficultly frangible, nor 
particularly heavy ; and is found along with 
quartz, opal, chalcedony, &c. at Kosemuctz, 
in Lower Silesia. 
Chrysopras is principally used for ring- 
stones, and some varieties are highly esteem- 
ed ; but it is difficult to cut and polish. 
Tzventy-ninth Species. Flinty Slate. 
This lias been divided into two sub-species, 
common flinty slate, and Lydian stone. 
First Sub-species. Common Flinty Slate. 
The principal colour is grey, but there are 
many varieties of shades. It occurs massive 
in w hole beds, and frequently in blunt-angled 
pieces, With a smooth and glimme ing sur- 
face. Internally, it is faintly glimmering 
more or less translucent on the edges ; hard, 
brittle, difficultly frangible, and not particu- 
larly heavy. 
It occurs in beds in transitive mountains 
in Saxony, at the lead-hills in Scotland, and 
other places. 
Second Sub-species. Lydian Slone. 
The colour is greyish-black, passing into 
velvet-black. It occurs massive, and is 
frequently found in trapezoidal-shaped rolled 
pieces. Internally, it is glimmering ; opaque, 
hard, pretty easily frangible, and not parti- 
cularly heavy. It is found in similar form- 
ations wfith the preceding, near Prague and 
Carlsbad in Bohemia, in Saxony, and in the 
Moorfoot and Pentland hills, near Eciin- , 
burgh. 
When polished, it is used as a test-stone 
for determining the purity of gold and silver; 
but is less suited for this purpose than basalt, 
and some kind of clay slate. 
Thirtieth Species. Cads Eye. 
The principal colour is grey, of which it 
presents many varieties. It occurs in blunt- 
edged pieces, in rolled pieces, and likewise 
massive. Internally, it is shining; usually 
translucent, and sometimes also semitrans- 
parent. It is hard, easily frangible, and not 
particularly heavy. 
Its geognostic situation is unknown. It is 
imported from Ceylon and Ihe coast ot Mala- 
bar ; and is usually cut for ring-stones. Some 
of the varieties are highly valued. 
Thirty-first Species. Prehnite. 
The colours are various shades of green, 
white, and yellow. It is sometimes massive, 
and sometimes chrystallized in oblique tour- 
sided tables. Externally, the chrystals are 
smooth and shining ; internally, inclining to 
glistening and pearly. 
Prehnite is translucent, sometimes passing 
into semitransparent and transparent : it is 
hard, easily frangible, and not very heavy, 
tt occurs in Dauphiny in veins ot the oldest 
formation ; in Scotland in rocks belonging to 
the newest floetz trap formation ; and was 
first discovered in Africa* by colonel Prehn, 
from whom it receives its appellation. 
