[357] Pliny’s five books (xxxiii-xxxvii) on mineralogy in his _Natural History_ are the chief source upon which later writers drew. An epitome of them, or rather, an epitome of an epitome, was made by Solinus in the third century. This underwent a further revision in the sixth century. Isidore is supposed to have used both the epitome and the original, as well as an unknown source, from which he drew the medical virtues of the precious stones. _Cf._ King, _The Natural History, Ancient and Modern, of Precious Stones_ (London, 1865), p. 6. ANALYSIS I. Kinds of earth (ch. 1). II. Earthy substances made out of water (_de glebis ex aqua_[358]) (ch. 2). III. Common stones (ch. 3). IV. The less common stones (ch. 4). V. Marbles (ch. 5). VI. Gems (chs. 6–15). 1. Green gems (ch. 7). 2. Red gems (ch. 8). 3. Purple gems (ch. 9). 4. White gems (ch. 10). 5. Black gems (ch. 11). 6. Parti-colored gems (ch. 12). 7. Crystalline gems (ch. 13). 8. Glowing gems (ch. 14). 9. Gold-colored gems (ch. 15). VII. Glass (ch. 16). VIII. Metals (chs. 17–24). 1. Gold (ch. 18). 2. Silver (ch. 19). 3. Bronze (ch. 20). 4. Iron (ch. 21). 5. Lead (ch. 22). 6. Tin (ch. 23). 7. Amber (ch. 24). IX. Weights (ch. 25). X. Measurements (chs. 26, 27). Abbreviations for units of measurement (ch. 27). [358] Asphalt, alum, salt, soda, etc. EXTRACTS Chapter 4. On the less common stones. 3. _Gagates_ (jet) was first found in Cilicia, thrown up by the water of the river Gagates. Whence it was named, although it is very abundant in Britain. It is black, flat, smooth, and burns when brought near to fire. Dishes cut out of it are not destructible. If burned it puts serpents to flight, betrays those who are possessed by demons, and reveals virginity. It is wonderful that it is set on fire by water and extinguished with oil. 19. _Amiantos_ (amianth) ... resists all poisons, especially those of the magi. Chapter 7. On green gems. 8. Certain believe that the jasper gives both attractiveness and safety to its wearers, but to believe this is a sign not of faith but of superstition. 9. The topaz is of the green sort and it glitters with every color. It was found first in an island of Arabia in which Troglodyte pirates, worn out with hunger and storm, discovered it when they pulled the roots of herbs. This island was sought for afterward, and was at length found by seamen, being all covered with clouds. And on this account the place and the gem received the name from cause. For τοπάζειν in the Troglodyte language denotes seeking.