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Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires

Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires Page of 251 Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires Text size:minus plus Restore normal size   Mail page  Print this page
BOOK I
11
Certain minerals are dense such as bitumen, stones, and metals while others are tenuous such as the spodos found in mines, natural lime, melan-teria, and a black mineral which resembles the down from plants and from which we obtain quicksilver (metacinnabarite). We apply the term dense to minerals which, because of strong coherence, occur in large units and apply the term tenuous to minerals which occur in small units because of the lack of coherence. Thus hard and tough minerals, since they occur in large units, are dense and soft and easily crushed minerals which occur in small units are tenuous. Impressions can be made in certain minerals of the latter class such as unctuous, incoherent, soft or moistened earths, bitu­men, lead. Stones and most minerals will not take impressions. Some min­erals soft enough to take impressions of the hand or blows of a hammer may be worked into various shapes while other minerals which are harder may be cast. Copper can be cast as well as worked by hammering. Some minerals, too hard to take impressions, are soft enough to be scratched by iron, for example, marbles, almost all rocks and many stones known by special names. Other minerals are too hard to be scratched such as flint and almost all transparent gems. Minerals soft enough to be scratched by iron may be engraved and even turned in a lathe, for example the Zeblician marble of Misena and the Comensis stone of Italy. Goblets are turned from the former and, according to Pliny, cooking utensils were turned from the latter. Venetian tofus can be cut with iron and rocks and marbles can be split with wedges. Some of the minerals which cannot be scratched with iron are very brittle such as flint while others such as the knots found in schistos and basaltes can be broken only with great effort. Some minerals, for example the diamond, are not affected by a blow.
Some gems are scratched by a file such as topazius (chrysolite) while others are not, such as lapis-lazuli and carbunculus. All gems can be en­graved with emery except the diamond which can only be scratched by its own fragments.
Certain minerals can be compressed such as native spodos and a black mineral similar to the down of plants and which is sometimes argentiferous, sometimes hydrargyriferous (metacinnabarite). Common stones, gems, rocks, marbles, and metals cannot be compressed. Porous, unctuous, soft earths can be compressed and when compressed, remain so. Some can be drawn out, i.e., protuberences of unctuous earths which have been moist­ened with water, as well as bitumen can be drawn out into a long thin body because these have the essence of movement. Earths which are hard, meager or dry cannot be drawn out. Gold, silver, and copper can be drawn as well as stamped. None of the stones can be drawn. Bitumen can be drawn and compressed. Some minerals are cleavable, for example selenite and talc, for the openings in these minerals have been extended along the length, not the width. Some occur similar to hair such as native silver and alum. A great many do not have a cleavage such as stones and metals. Some minerals burn readily, sulphur, bitumen, and jet, while metals,
Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires Page of 251 Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires
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