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BOOK V
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87
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Sulzbach. In any locality where one finds hematite and schistos one
will also find red rocks and earths from which, as a source, these
minerals are formed. Dioscorides writes that hematite is found in the
red ocher of Sinope. Schistos occurs in Spain, hematite in Arabia, Egypt, Africa and Ethiopia.
Each
mineral varies in color. They may be similar in color to dried blood,
hence the name, or they may imitate the color of iron and at times the
surface may even have the color of saffron. The latter material is
found in Misena. A variety that is entirely black is mined not far from
the mountain named for the silver birch, as I have just mentioned.
Sotacus relates that a variety of black schistos is found in Africa and from its resemblance to quenched coal is known as anthracites. Schistos is
usually smooth on the outside and as brilliant as polished iron, for
example, that from Misena which is the hardest of all. It is less
brilliant inside. Some is not brilliant externally but sparkes on the
inside like the artificial minium the painters call cinnabaris. Mineral
of this variety occurs in the Harz forest. This same material, when
pulverized, sparkles as though it had been adulterated with mercury.
I
shall now take up the colors produced by both of these minerals when
rubbed on flint and the colors they have after being burnt. Some
produce a streak with ease, as is usually the case, while others, for
example the material from Arabia and Misena, give a streak with
difficulty because of their excessive hardness. Although they commonly
give a blood-red streak the material from Africa called anthracites gives
a black streak from the bottom portion and a yellow streak from the
rest. Similarly the material from Goslar that has congealed in the
form of grapes gives a black streak from one part and a dark yellow
streak from another. The Arabian hematite has a color similar to
saffron. Both schistos and hematite, if they have congealed
with a color similar to blood, imitate the color of cinnabar after they
are burnt and if they are black burning will deepen the color. Burning
turns all other varieties of schistos to a florid color. Both hematite and schistos draw the tongue together. Although each is dense and usually hard the more the luster of schistos approaches
the luster of iron the harder it is, for example, that found in Misena
and the Harz forest. Some knots are found in Misena the size of walnuts
and so hard that when placed upon an anvil they are unaffected when
struck. Silversmiths polish these hard pieces and then, in turn, use
them to polish very thin pieces of gold foil by drawing the foil over
the stones. They also use them to polish the foils they place beneath
gems in order to improve the color of the gem with the color of the
foil. In each case the stones are fashioned into various shapes.
Hematite
almost always occurs in the form of lumps and may be full of little
hollows as is that from Hildesheim. The Harz mineral sometimes congeals
in the form of grapes. Schistos shows a much greater variety of forms. It may be wedge-shaped at either end or both. Sometimes it is
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