Alabaster
ALABASTER, a name applied to two distinct mineral substances,
the one a hydrous sulphate of lime and the other a carbonate of
lime. The former is the alabaster of the present day, the
latter is generally the alabaster of the ancients. The two
kinds are readily distinguished from each other by their relative
hardness. The modern alabaster is so soft as to be readily
scratched even by the finger-nail (hardness= 1.5 to 2), whilst
the stone called alabaster by the ancients is too hard to be
scratched in this way (hardness=3), though it yields readily to a
knife. Moreover, the ancient alabaster, being a carbonate,
effervesces on being touched with hydrochloric acid, whereas the
modern alabaster when so treated remains practically unaffected.
Ancient Alabaster. -- This substance, the ``alabaster of
scripture, is often termed Oriental alabaster, since the early
examples came from the East. The Greek name alabastrites is
said to be derived from the town of Alabastron, in Egypt,
where the stone was quarried, but the locality probably owed
its name to the mineral; the origin of the mineral-name is
obscure, and it has been suggested that it may have had an Arabic
origin. The Oriental alabaster was highly esteemed for making
small perfume-bottles or ointment vases called alabastra;
and this has been conjectured to be a possible source of the
name. Alabaster was also employed in Egypt for Canopic jars
and various other sacred and sepulchral objects. A splendid
sarcophagus, sculptured in a single block of translucent
Oriental alabaster from Alabastron, is in the Soane Museum,
London. This was discovered by Giovanni Beizoni, in 1817, in
the tomb of Seti I, near Thebes, and was purchased by [[Sir John
Soane]], having previously been offered to the British Museum.
Oriental alabaster is either a stalagmitic deposit, from the
floor and walls of limestone caverns, or a kind of travertine,
deposited from springs of calcareous water. Its deposition
in successive layers gives rise to the banded appearance which
the marble often shows on cross-section, whence it is known as
onyx-marble or alabaster-onyx, or sometimes simply as onyx -- a
term which should, however, be restricted to a siliceous
mineral. The Egyptian alabaster has been extensively worked
near Suez and near Assiut; there are many ancient quarries
in the hills overlooking the plain of Tell el Amarna. The
Algerian onyx marble has been largely quarried in the province of
Oran. In Mexico there are famous deposits of a delicate green
variety at La Pedrara, in the district of Tecali, near Puebla.
Onyx-marble occurs also in the district of Tehuacan and at several
localities in California, Arizona, Utah, Colorado and Virginia.
Modern Alabaster -- When the term ``alabaster is used
without any qualification it invariably means, at the present
day, a finely granular variety of gypsum. This
mineral, or alabaster proper, occurs in England in the
Keuper marls of the Midlands, especially at Chellaston in
Derbyshire, at Fauld in Staffordshire and near Newark in
Nottinghamshire. At all these localities it has been extensively
worked. It is also found, though in subordinate quantity, at
Watchet in Somersetshire, near Penarth in Glamorganshire, and
elsewhere. In Cumberland and Westmoreland it occurs largely
in the New Red rocks, but at a lower geological horizon.
The alabaster of Nottinghamshire and Derbyshire is found in
thick nodular beds or ``floors, in spheroidal masses known
as ``balls or ``bowls. and in smaller lenticular masses
termed ``cakes. At Chellaston, where the alabaster is known
as ``Patrick, it has been worked into ornaments under the name
of ``Derbyshire spar -- a term applied also to fluorspar. The
finer kinds of alabaster are largely employed as an ornamental
stone, especially for ecclesiastical decoration, and for the
rails of staircases and halls. Its softness enables it to be
readily carved into elaborate forms, but its solubility in
water renders it inapplicable to outdoor work. The purest
alabaster is a snow-white material of fine tiniforni grain,
but it is often associated with oxide of iron, which produces
brown clouding and veining in the stone. The coarser varieties
of alabaster are converted by calcination into plaster of Paris, whence they are sometimes known as ``plaster stone.
On the continent of Europe the centre of the alabaster trade is
Florence. The Tuscan alabaster occurs in nodular masses,
embedded in limestone, interstratified with marls of Miocene
and Pliocene age. The mineral is largely worked, by means
of underground galleries, in the district of Volterra.
Several varieties are recognized -- veined, spotted, clouded,
agatiform, etc. The finest kind, obtained principally from
Castellina, is sent to Florence for figure-sculpture, whilst
the common kinds are carved locally, at a very cheap rate, into
vases, clock-cases and various ornamental objects, in which
a large trade is carried on, especially in Florence, Pisa and
Leghorn. In order to diminish the translucency of the alabaster
and to produce an opacity suggestive of true marble, the
statues are immersed in a bath of water and gradually heated
nearly to the boiling-point -- an operation requiring great
care, for if the temperature be not carefully regulated, the
stone acquires a dead-white chalky appearance. The effect of
heating appears to be a partial dehydration ofthegypsum. If
properly treated, it very closely resembles true marble, and
is known as mormo di Castellina. It should be noted that
sulphate of lime (gypsum) was used also by the ancients, and was
employed, for instance, in Assyrian sculpture, so that some
of the ancient alabaster is identical with the modern stone.
Alabaster may be stained by digesting it, after heing
heated, in various pigmentary solutions; and in this way a
good imitation of coral has been produced (alabaster coral).
Initial text from 1911 encyclopedia