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BOOK V
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97
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is
free from all adhering earth it may be as white outside as inside. When
split open it is light inside and glistens like marble and in some
cases the outside also has a high luster. Having been powdered on a
whetstone, as is customary since it is used in medicine, it has no
taste. A piece the size of a chick-pea drunk with about a half ounce of
hot water is prescribed in cases of difficult urination since it
destroys gall-stones, more especially those in the kidneys than in the
bladder.
Trochites is related to lapis judaicus and
takes its name from a wheel. Since nature has given it the form of a
drum the round part of it is smooth and each side has a certain degree
of smoothness. Radii, so prominent they form striations, extend in all
directions from the center to the outer rim like spokes in a wheel. It
varies much in size but the smallest is about one tenth the size of the
largest. The largest is the width of a finger in diameter and a third
as thick. The color varies being either gray, black or yellow. This
variety of colors is due to the contamination of earth since in the
interior it is whiter than the rest of the material. It breaks, similar
to lapis judaicus, along the length, width and obliquely and is
smooth and brilliant inside. Having been placed in vinegar it gives off
bubbles like astroites and sometimes possesses the same power to move itself from one place to another. Entrochos is sometimes formed from trochites by being built up of two, three, four or even more since as many as twenty are found joined together. There are two species of entrochos, one
evenly rounded, the other evenly rounded but with the central part
thickened and the edges constricted. These have the prominent radiating
lines characteristic of trochites where two parts join on the curve of the girdle although the lower portions lack a girdle and are entirely smooth. The trochites are
joined in such a fashion that the radii of one fits into the striae of
the other. The thickened species usually have radii extending almost to
the center. Often a shapeless stone is found associated with these
minerals which contains within itself the form of a wheel which has
remained in the stone as though it were the root of the mineral that
had been broken off. These minerals occur in Saxony near Hildesheim on
the last peak of Mt. Maurice in groups in a whitish yellow marble and
in a glutinous earth; between Alfeld and Embach; in Hesse on that part
of the Cnoreberg hill which is near the mountain where the fortified
city of Spangenberg is located.23
Some
stones found in the fields may have prominent lines and striae and the
ignorant believe that these fall when it thunders. For this reason the
Greeks call them brontia. They resemble the head of a tortoise. If they fall when it rains they are called ombria. Ours
are light yellow, green, red, yellowish red and even with variegated
colors. When polished they will reflect an image like a mirror. They
are almost always in the form of a hemisphere, rarely oblong,
sometimes the size of an egg but usually smaller. Some have two circles
which appear to be units of measure. Five promi-
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These minerals are fossil crinoid stems.
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