Semi-weekly standard. [volume] (Raleigh, N.C.) 1853-18??, 1863-06-09
For the Standard.
For the Standard.
Clays; their Origin, Composition and Uses.
BY E. EMMoNs, STATE GEoLoGIsT

r.. BY E. EMMoEs STATE GEoIoaBT.
Clay, in the nomenclature of geologsts, is rock,
though soft and destitute of some of the most str-
king physical characteristics which rocks are sup
posed TO possess. As rocks, however, their origin
mas been subsequent to all those masses which are
strictly primary or formed anterior to organic be-
ngs: Clays are then secondary in respect to their
origin being derived invariably from pre-existing
materials. They are produced by the influence of
atmospheric forces. acting upon solid masses, as
granite, gneiss and mica and talcose states. OF
these forces carbonic acid and water are among the
most energetic. Bodies, however, which are com.
pleX in their composition, are unstable and it seems
as II their elements were struggling to breakup
their old combinations and form new compounds
more simple and stable in their arrangements
linus we tind many GRANTEES undergoing radical
changes being resolved ultimately into clay, sand
and oxides Of the metals These are stable bodies,
being neutral in all their relations to the ordinary
forces of nature. Water acts chemically and me-
chanically. In the former capacity it dissolves
large number of bodies; in the latter it breaks up
IN freezing the most cohesive rocks, and ultimately
reduces them to powder. 1t thus prepares the way
for the joint chemical action of itself and carbonic
acid. In these arrangements we cannot fail to re-
cognlze the most important provision for the sus-
tena1ce of the vegetable and animal kingdoms.
The clays, considered geologically, may belong to
the most ancient or the more recent formations and
it is only by investigating their relations to other
rocks or BY their organic remains that their relative
ages can be determined. Clays are still forming by
the influence of the forces have already referred
to. KaoliDs, SO much esteemed for porcelain, are
forming to-day from the coarse GRANTEES of our
mountain chains Clay is usually found in beds;
the most important exception occurs in the CLAWS of
vein assures or the lodes of metals. II is the
.ttuccdn of miners. These beds are commonly found
IN depTosions of the earth's surface or in valleys
where they are exposed to view on tho banks of
rivers and creeks But certain kinds of clay belong
to mountainous districts, the Kaolin already re-
ferred to. Although granite and other allied COM
pounds are prolific source of clay, yet there are
many others. Chemists have shown that alumine
IS one OF the most common elements in the mine
raj kingdom All rocks, except the pure sandstones
and limestone, contain alumine, and by far the
greater proportion of the earthly minerals contain
alumine as essential constituent; it is therefore
one of the most widely diffused bodies in the min
eral kingdom. But alumina and clay are not iden-
ticM bodies. Aumine is the pure oxide of the
metal aluminium. If it is wished to know what
this pure body is, make a solution of one part of
alum in SIX parts of boiling water, and then add
solution of carbonate of potash or common pearl
ash A white bulky precipitate is separated; this
is alumna or alumine of chemists. 1t is not how
ever, properly clay; it is the basis of clay. When
it combines with silex it becomes clay, and its
properties are totally changed. Hlumine is light
hoculent body, scarcely plastic or susceptible of
being moulded, but in combination with slick body
highest sense plastic and mouldable 1t takes any
shape under the hand of the potter, and being en-
trey unelastc retains the most delicate impression
or figure which may be inscribed upon it.
The beds of clay which have been referred to- are
not strictly beds of alumina but in the techninal
language of chemists, are silicates Of GluminG.-
The best idea we can get of silex, is that in the
mass of fine quartz crystal. Under favorable con-
ditionS, this substance combines with alumine and
forms variety Of clay. In addition, however, to
this chemical union of sileX and alumine, there is
usually mixture of sex in the condition of sand,
which is variable quantity. This additional mix
ture of sand modifes, as we shall see, the proper
ties of clays, and fit them for greater variety of
purposes. Pure alumine is rare in nature and is
known in the sapphire and ruby gems which rank
next in hardness and value to the diamond
Clays are frequently impure from the presence
of iron, which may be known by its red or yellow
ish color, or by combination with carbonates of
lime and magnesia, the presence of which may be
known by their effervescing with acids. These
bodies also modify the properties of clay, and may
spoil it for fine pottery, or they may not be at all
detrimental to it when employed for other purposes
1t is difficult to give satisfactory classification of
elays. A distinguished French chemist classifes
them under the terms freprOof tasible eGlcareousi
and TeTTugin0uS names which indicate in part,
certain properties as well as certain combinations.
The origin Of clay may as basis for CLASH
fication Thus the GRANTEES give origin to all the
Kaolins, while the states furnish directly the plastic
pipe clays and probably fullers earths. 1t is true
the slate clsys may have been derived originally
from the GRANTEES and their allied compounds, for
slate bing sedimentary rock, may have been also
derived from these older rocks. For practical
purposes the division Of clay into lsi5le and infu
sibe is the most important division. But eshould
remark the terms are relative; by infusible is really
meant great difficulty in fusion not impossiblity,
for by the nstrumentality of the proper heat which
may be dexterousy applied, all bodies fusible.
Having made the foregoing preliminary remarks,
shall proceed in the next communication to speak
of the composition and localities Of the Kaolns of
North Carolina.