Crystal is a bright stone and clear, with watery colour. Men trowe that it is of snow or ice made hard in space of many years. This stone set in the sun taketh fire, insomuch if dry tow be put thereto, it setteth the tow on fire. That crystal materially is made of water, Gregory on Ezekiel i. saith: water, saith he, is of itself fleeting, but by strength of cold it is turned and made stedfast crystal. And hereof Aristotle telleth the cause in his Meteorics: there he saith that stony things of substance of ore are water in matter. Ricardus Rufus saith: stone ore is of water: but for it hath more of dryness of earth than things that melt, therefore they were not frozen only with coldness of water, but also by dryness of earth that is mingled therewith, when the watery part of the earth and glassy hath mastery on the water, and the aforesaid cold hath the victory and mastery. And so Saint Gregory his reason is true, that saith, that crystal may be gendered of water. In old time or the use of iron was known, men eared land with brass, and fought therewith in war and battle. That time gold and silver were forsaken, and gold is now in the most worship, so age that passeth and vadeth changeth times of things. Brass and copper are made in this manner as other metals be, of brimstone and quicksilver, and that happeneth when there is more of brimstone than of quicksilver, and the brimstone is earthy and not pure, with red colour and burning, and quicksilver is mean and not subtle. Of such medlying brass is gendered. Electrum is a metal and hath that name, for in the sunbeam it shineth more clear than gold or silver. And this metal is more noble than other metals. And hereof are three manners of kinds. The third manner is made of three parts of gold, and of the fourth of silver: and kind electrum is of that kind, for in twinkling and in light it shineth more clear than all other metal, and warneth of venom, for if one dip it therein, it maketh a great chinking noise, and changeth oft into divers colours as the rainbow, and that suddenly. Heliotrope is a precious stone, and is green, and sprinkled with red drops, and veins of the colour of blood. If it be put in water before the sunbeams, it maketh the water seethe in the vessel that it is in, and resolveth it as it were into mist, and soon after it is resolved into rain-drops. Also it seemeth that this same stone may do wonders, for if it be put in a basin with clear water, it changeth the sunbeams by rebounding of the air, and seemeth to shadow them, and breedeth in the air red and sanguine colour, as though the sun were in eclypse and darkened. An herb of the same name, with certain enchantments, doth beguile the sight of men that look thereon, and maketh a man that beareth it not to be seen.