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Book VII marbles, gems in rings and other applications

Book VII marbles, gems in rings and other applications Page of 251 Book VII marbles, gems in rings and other applications Text size:minus plus Restore normal size   Mail page  Print this page
BOOK VII
159
According to Xenophon it was made into millstones by the inhabitants of that district and brought to Babylon.
Lapis molaris which melts in a fire is called μύλη by Aristotle and Varro who has described the revolving millstones of Vulsiniis. The stones that do not melt are called μυλίαν. Theophrastus and Strabo called the stones that melted μυλίαν, physicians called them μυλίτης, and those who followed the Latin nomenclature molaris. Certain Greek writers called them pyrites since fire can be drawn from them just as from hard pyrite. Usually these stones are quite hard. The black gem that burns the fingers when heated by rubbing is evidently pyrites. Since this stone is unaffected by rain, heat or cold it can be used as a building stone. Millstones are made from it whence comes the name. According to Pliny there are certain mill­stones belonging to this genus that, when polished with flint and viewed from a distance, have the appearance of ophites. Commonly molaris is black and sometimes spotted since it has formed from a liquid material of this color. Actually if a reddish stone is melted to a liquid the part that will flow becomes black when it congeals. Aristotle writes that this materi­al is similar to limestone and of course limestone can be used as a building stone but as Pliny writes, this has a certain natural unctuousness. When free of pyrite it is used for millstones. It reduces swellings that may have come on any external part of the body.
But to return to arenaceous rocks. Sand can be obtained from them when they are crushed finely but this is not the only source of sand. It is also obtained from the stones used in the manufacture of glass as I have explained in Book V, from stony marl, from unctuous limestone, and, in fact, from almost all stones and rocks that have a similar hardness. They make a variety of sand that is called carbunculus from bituminous earth that has been changed into a rather soft rock.
There are three genera of sand. The first is sedimentary sand that is dug from pits such as those at Pelgrana, Misena, and Glogova, Lygius. The second is fluvial that is found along rivers and streams. The third, marine that is found on beaches and seashores. Pliny describes sand that was obtained from the shallows of the Adriatic Sea when exposed during the summer. Sands vary in color according to the color of the rocks from which they are derived. That from Pelgrana is white, that from Glogova, yellow. The sand from Mt. Peribolos, Rome, is a golden color and for that reason they have come to call the mountain Motorius, i.e., golden moun­tain. Fluvial sand is usually gray although red, black and other colored sands do occur.
Some sand is fine, some coarse. The fine usually comes from pits. The fluvial and marine is usually coarse and mixed with gravel that must be separated with a sieve. It may even contain a large amount of coarse gravel. The sand that is to be mixed with lime must be free, not only of fine and coarse gravel but also of all earth and congealed juices. Earth affects the tenacity and toughness of lime and destroys its power to hold
Book VII marbles, gems in rings and other applications Page of 251 Book VII marbles, gems in rings and other applications
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