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20
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DE NATURA FOSSILIUM
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tained
metallic particles a mixed earth when it is actually a composite earth.
But it behooves one who teaches others to give exact names to
everything.
An
earth and a juice do not form a mixed mineral if the former absorbs the
liquid, surrounds the congealed juice, or adheres to it. The juice can
always be washed out and at times even removed by hand. But a stone and
a juice can produce a mixed mineral when a solid is created from
material of each one, even if sometimes if retains the appearance of
one of them. Many mixed minerals form from an earth and a metal and
even more from a stone and a metal. Several mixed minerals contain a
stone, juice, and metal. Thus we see that there are four forms of mixed
minerals which again, as genera, are divided into species.
When
two simple substances form a mixed mineral they may be combined in
equal or unequal proportions. When combined in equal proportions they
form one genus and combined in unequal proportions they form two, since
sometimes one substance predominates, sometimes the other. According to
that reasoning three genera may be found which contain a metal and a
stone, however, only one of these genera has been found that contains
an earth and a metal, namely, the third genus which contains more
metal than earth. I believe that the first genus with equal parts of
metal and earth and the second with more earth than metal have never
been found. Only the first and third genera of mixed minerals which
contain a stone, congealed juice, and metal are found. This class of
mixed minerals is formed from these simple things in such a manner that
the mixture contains abundant metal and more congealed juice than
stone. This refers to mass not weight since the mixture might have a
greater mass of congealed juice than metal and yet the metal could have
the greater weight.
Since
the third genus is divided into three parts, there are six genera of
mixed minerals and each of these contains many species. The first genus
which forms from stone and congealed juice embraces Tusculum flint,
Sabine stone, and many others. The second genus contains a metal and
earth, the third has equal parts of stone and metal, the fourth is rich
in metal, the fifth, with an abundance of stone embraces gold, silver,
and copper ores. The sixth genus includes sulphurous pyrite and
bituminous cadmia which contain other metals. The older Latin
and Greek writers have not recognized the natures of many mixed
minerals, or if they did, they have not described them sufficiently.
They have called the forms of these either stones, such as pyrite, cadmia, and
galena, or veins of gold, silver, and copper, since they did not
distinguish between composite and mixed. I shall not say more now about
these things but will take up the earths, both simple and mixed.
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