Earths. MINERALOGY. Earths. 
452 
Order IV. ARGILLACEOUS EARTHS. 
, Thefe confifl principally of aluminous earth ; and the 
chief and leading genus is Aluminaris, or alumine, 
which is the bafis of alum. See Alum, vol. i. and, for 
the chemical properties and artificial preparation of this 
earth, fee the article Chemistry, vol. iv. p. 221. The 
following are the generic charadlers. 
Aluminaris. —Confining almoft entirely of alumine : 
•meagre to the touch, light, without lullre, earthy, ad¬ 
hering a little to the tongue, ftaining a little ; nearly fo- 
lubie in nitric acid, contracting and hardening in the 
fire, emitting fparks before the blow-pipe. 
Aluminaris nativa, or native alumine, is faid to be 
found in various parts of Britain, Mufcovy, and Saxony, 
in kidney-form mafles: lhow-w'hite, very foft, breaking 
into indeterminate fragments, and does not readily diffufe 
itfelf in water. This earth is a conftituent part of the 
fait called alum; from a lblution of which it may be con¬ 
veniently obtained, nearly in a Hate of purity; and hence 
its prefent name. It is alfo a principal conftituent part 
of clays, or natural argillaceous compounds. 
Dr. Kidd, profefibr of chemiflry at Oxford, obferves 
that the exiftence of native alumine is nearly as queflion- 
able as that of native lime. An earthy fubftance, faid to 
be native alumine, and often met with in cabinets in 
finall kidney-formed nodules of a very white colour, was 
Lome time fince difeovered near Halle in Saxony; but, as 
it was found, according to common report, in a piece of 
ground attached to a chemical laboratory, many mine- 
ralogifls doubted its natural origin; and luppofed it to 
be an artificial preparation, which had been thrown afide 
after the completion of the experiments that had given 
rile to its production. Mr. Jamelon however fays, that 
from its form, and the fituation where it is found, it ap¬ 
pears to have had a natural origin : and that no labora¬ 
tory is nearer the fpot than a quarter of a league. Yet, 
from the analyfis he gives of it, it might be inferred that 
this fubltance is not a natural production: and Dr. Kidd 
concludes that it is not entitled to be conlidered as a 
fpecimen of native alumine. 
Arcilla, Clay.—Confifting of alumine and flex, with 
generally fome oxyd of iron and inflammable matter : 
opake, without lullre, of a common form, foft to the 
touch ; earthy, lightilh, foft, imbibing and retaining wa¬ 
ter and oil, by each of which it is loftened, and rendered 
plaltic by the former, and emitting an earthy lined; not 
effervefeing with nitric acid ; contracting and becoming 
harder in the fire. There are thirty-one lpecies. 
1. Argilla porcellana, or porcelain-clay: meagre, w'hite, 
friable, adhering to the tongue, becoming white when 
burnt, and in a very llrong heat forming porcelain. Found 
in Cornwall, Japan, China, Saxony, and various parts of 
Europe; and is luppofed to originate from decompofed 
fellpar. Colour white, greyilh, reddifh, or yellowifh- 
white: adheres very llightly to the tongue, and feels 
foft, but not greafy: does not change its colour w'hen 
expofed to heat, but becomes white, and tranfparent in 
proportion to the quantity of filex it contains. It is prin¬ 
cipally uled in the manufacture of china ware. Contains 
alumine 60, lilex 20, air and w'ater 12. The clay of which 
the Berlin porcelain is made, is found below Halle, in 
the diflriCl of Magdeburg: that of which the Aullrias 
porcelain is made, at Paffau. The French porcelain-clay 
is met with in the vicinity of Limoges. 
If clay, which otherwife -would be fit for making porce¬ 
lain, contain one tenth part of lime, it is fufible in the 
heat to which the porcelain mull neceflarily be- expofed, 
and conlequently unfit for the purpofe intended. It may 
contain as much as one twentieth part without occafion- 
ing the vitrifaClion of the mafs. Oxyd of iron is inju- 
r.uus in a double lenfe ; for it not only promotes vitri- 
faCtion, but diflcolours the porcelain by the alteration it 
undergoes during the procefs of baking. An inferior 
kind of porcelain-clay is found in that part of Bovey- 
heath, in Devonlhire. which is near the London road : it 
is met with not much below the furface of the earth ; and, 
from a confideration of its fituation and the attendant 
circumllances, appears evidently to be a natural depofi- 
tion of earthy felfpar. Whoever confiders the fwampy 
nature ofthat heath, the appearances oblervable on its fur- 
face, and its relative fituation to the adjoining granite- 
hills, may eaflly be convinced that it is derived from the 
detritus of thefe, walhed down and depofited by water 5 
for this heath is as it were a natural bafon, which mull ne- 
ceftarily receive whatever is brought down from the ad¬ 
joining high ground ; and its furface in a great meafure 
conlills of a white fandy quartz and occalional cryllals 
and fragments of felfpar, that evidently correfpond with 
the quartz and unaltered fellpar of the neighbouring 
granite. 
2. Argilla leucargilla, or pipe-clay : very foft and greafy 
to the touch, adhering to the tongue, Ihining when rub¬ 
bed, becoming firft blackifh and paler when burnt, apy- 
rous. Found in Normandy, near Cologne, Livonia, and 
other parts of the world. Colour varying from pure 
white to black, and is often variegated; when firft ex¬ 
pofed to heat, it becomes blackilh, from the inflammable 
matter it often contains, but by continued.heat it turns 
pure white ; it is ufed for tobacco-pipes and various vef- 
lels. As to its conftituent parts, it fcarcely differs from 
porcelain-clay; but the filiceous particles are not fuffi- 
ciently fine to render it applicable to the fame purpofe. 
3. Argilla lithomarga, or potters’ clay: potters’ clay 
does not differ materially from pipe-clay. It frequently 
contain a greater proportion of lime and of oxyd of iron; 
and hence is more liable to vitrify, and to be difcoloured 
by the application of the higher degrees of heat; on 
which account it is employed in the compofition of the 
inferior kinds of earthen-w-are or pottery; and is called, 
in confequence, potters' clay. 
The fituation in which potters’ clay is found, and its 
general appearance and charadler, afford probable grounds 
for fuppoling that it has been formed, in the manner de- 
feribed in the preceding pages, by the depolition of the 
finer parts of difmtegrated rocks of various kinds. Thofe 
which contain leaft iron have been probably derived from 
granite and its varieties: thofe which contain mofl, from 
bafalt perhaps, and rocks of that genus. 
4. Argilla fullonica, or fullers’ earth : this earth, which 
is commonly of a dark drab-colour with an obfcure fhade 
of green, is not dudtile, like common clay, when mixed 
with water; but rather crumbles into a pow'der iike marl. 
It is alfo nearly friable; and does not adhere to the 
tongue. The fullers’ earth of the iflandof Cimolus, ana- 
lyfed by M. Klaproth, was brought over from thence by 
Mr. Hawkins. Similar fpecimens were alfo brought from 
a neighbouring ifland : and in both inflances numerous 
grains of quartz were difleminated through the mafs. 
Fullers’ earth is met with in France, Saxony, and Sweden ; 
and in very great abundance in different parts of England, 
as at Woburn, Ryegate, and Maidllone. A great.propor- 
tion of the fullers’ earth of commerce comes from Hamp- 
fliire. 
The fpecific adlion of fullers’ earth depends on the 
alumine contained in it; and it appears that the propor¬ 
tion of this fhould not be lefs than a fourth or fifth of 
the whole mafs. It fhould not however be much more ; 
for in that cafe the fullers’ earth would be too tenaceous 
to diffufe itfelf through water. The filex alio fhould be 
in a very minute Hate of divifion ; otherwife the particles, 
being too rough, would wear out the texture of the cloth 
to which it was applied. M. Klaproth found that the 
earth from Cimolus poflefied the fulling property in a 
fuperior degree to the Englifh. 
5. Argilla cruflacea, or frofled fuller’s earth : greafy, 
lamellar, falling into finall pieces in water, and frothing 
when agitated, before the blow-pipe melting into a fpu- 
midcinereous glafs. Found on Mount Ofmund in Sweden. 
6. Argilla Lemnia, or Lemnian earth: greafy, ihining 
by 
