532. There is not merely a single silicious mineral, but many such, just as in clay, talc, and calx. How, then, do differences occur in these earths? When we survey the science of Mineralogy we remark that most minerals are composed of several earths; with them also metals, coal, sulphur, alkalies and acids are frequently associated. It follows thereupon that the further distinctions are no longer of an _internal_ kind, namely, alterations of substance; but proceed from combinations and thus indicate stöchiometric bodies. The next division of the orders I call _Families_. Order 1. _Silicious_ minerals. * 533. With how many bodies now can the silicious earth combine? It will first of all appear in a pure condition, as in quartz; then, in the next place, combine with the other earths, thus with clay, talc and calx. We have thus four families of _Earth-silices_. Fam. 1. Pure-Silex Quartz. 2. Argillaceo-Silex Zircon. 3. Talco-Silex Emerald. 4. Calcareo-Silex Leucite. 534. Thus the hardest minerals or the silicious precious stones are here placed. But these are obviously not exhausted with the above four combinations, but more of the latter must still be sought for. Those bodies which rank next to the earths, and can therefore enter into the following combinations are the other mineral classes, such as the salts, Inflammables, and metals; and we accordingly obtain the following _silicious_ minerals, as constituting _classes_. Fam. 5. Salt-Silex Topaz. 6. Inflammable-Silex Diamond. 7. Ore-Silex Garnet. 535. Still all the silicious minerals are not exhausted with these combinations. But now the silicious earth can combine with nothing more than the _elements_, whence three families originate. Fam. 8. Water-Silex Hornstone, Silicious schist, Jasper, Flint, Opal. 9. Air-Silex Silicious sinter, as Tripoli and Polierschiefer. 10. Fire-Silex Obsidian with Pitchstone, Pearlstone and Pumice. 536. Upon casting a glance at this series, it is shown, that the first seven families occur in a crystalline, but the last three only in a compact or structureless condition. The latter occur at the same time in large masses, the former, on the contrary, but scantily dispersed. The first family or the quartz, occurs as well in a compact and massive state as crystallized; the others, on the contrary, taken collectively, are only crystallized, and scarcely form small rocks here and there, but never mountain-chains. They are the precious stones proper, both on account of their hardness, as also their rarity. Precious stones are thus only combinations of silex with other earths, and with the classes; on the contrary, the elemental silices only, viz. the earth-, water-, air-and fire-silices, are massive.