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90
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DE NATURA FOSSILIUM
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friable
that it can be pulverized between the fingers. Hard material is burned
by the inhabitants of the Harz forest and Thuringia and after being
burnt is ground. They then mix this with water and use it instead of
chalk since it is more tenacious. The Phoenicians, Syrians and others
have all burnt and used gypsum at various times. Irrespective of the
original color it is always white after burning. Since it is glutinous
it retains heat within itself for a long time after being burnt as does
limestone. In the same manner gypsum is made from selenite (lapis specularis) after
having been burnt and this is the best. When burnt gypsum is mixed with
water it has the color of milk. When preparing it they pour the water
over the powder and stir it with wooden spoons in order to mix it well.
They do not use their hands as one cannot stand the heat. Having been
wetted, Pliny writes, it is used immediately since it sets and dries
very rapidly. It can be crushed and reduced to a powder a second time.
If moistened and allowed to stand over night it becomes so hard that an
ax must be used to break it. After wetting it a second time with water
it can be used to cement rough stones, as a whitewash and in arenas.
The small figures for buildings and the images of saints are made both
from burnt and wetted gypsum and carved from the natural mineral,
especially that which is similar in color to ivory. Pliny writes that
Lysistratus of Sicyon, brother of Lysippus, was the first to sculpture
the figure of man from this mineral and then cover the figure with wax
to free it from any imperfections.6 At Northusa in Thuringia
a gray wall has been built from the gypsum that occurs in beds in the
vicinity and the wall of the port of Algiers, a town of Mauretania,
Africa, is of similar material. Pliny writes that the sourness of wine
is reduced through the use of African gypsum. Theophrastus writes that
fullers have used this mineral instead of cimolian earth at various
times for preparing animal skins. It dries when used as a remedy and
has the power of producing a film over anything. For that reason it
stops the flow of blood when mixed with the white of an egg. Having
been burnt and thus made more tenuous it dries more but is less able to
produce a film over anything. When drunk it is fatal since it blocks
the veins and causes acute constipation.
Selenite (lapis specularis) is related to gypsum.6 It forms from limestone
6 Lysippus was a celebrated metal worker who lived in the latter part of the 4th century, B.C.
6
In modern usage gypsum is a generic name and selenite a specific name
given to gypsum occurring in transparent discrete crystals. Agricola
uses these names in much the same sense in his writings. Many of the
older writers confused gypsum and mica and Agricola is probably the
first to clearly distinguish the two minerals. It is interesting to
note that in Interpretatio he describes lapis specularis as unser lieben frawen eis-spar. Itali lumen de scaiola. Today the name eis-spath is
given to mica and Werner gave this name to sanidine feldspar. The
following reference to gypsum is given in Bermannus, page 456,—
Naevius. "But you do not recognize gypsum and lapis specularis which you have
already mentioned.
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