SILICON } CARBON } These elements will combine permanently with the BORON } principal gases. ALUMINA } These elements, when dissolved in certain acids, MAGNESIA } yield a _colourless_ solution. SULPHUR } MANGANESE } These elements, dissolved in acids, yield a _coloured_ IRON } solution. GOLD } DELESSITE is a chloride of iron. SILICA comprises only 2 species:—1. Quartz; 2. Opal. From _Quartz_, come Rock-crystal } Cairn-gorums } which are “_vitreous_,” Sand } and Chalcedony } Agate } Onyx } Carnelian } which are “_concretions_.” Sard } Bloodstone } Jasper } Flints } _Opal_ is a “hydrate” of SILICA, containing 7 per cent. of water. Precious, or “noble.” Iridescent. Common (colourless). “_Silicates._” Of Alumina { Feldspar. { Kaolin. { Emerald. Of do. with Glucina { Beryl { Garnet { Pyrope, or “precious garnet.” { Chrysolite. Of Magnesia { Meerschaum. { Asbest. Of do. with Fluorine { Topaz. { Tourmaline. Of do. with Zircon { Jargoon, or “Hyacinth.” The colour of “emerald” is due to the oxide of chrome; that of “beryl” to the oxide of iron. CARBON comprises only 2 species:—1. Diamond; 2. Graphite. “Diamond” is a perfect crystallization, and is the hardest substance known. “Graphite” (sometimes called “Black-lead”) is a carbonate of iron. The iron, however, enters in very small quantities, and is now supposed to be _accidental_. “Graphite” is a concretion, and is never met with in the form of crystals. “_Carburets._” Of Hydrogen { Bitumen. { Coal. Bituminized wood is Lignite, which, when very compact, is Jet. “Amber” is a vegetable resin. It is obtained from rivers in Sicily, and from mines in Russia. “Carbonates” of Lime { Limestone. { Calc-spar. { Chalk. The “marbles” of Paros and Carrara are _crystalline_ Limestone: those of Siena are _compact_ Limestone. ALUMINA comprises 2 species:—1. Corundum; 2. Sapphire. 1. “Corundum” is a very hard crystal, the common type of all the Sapphires. 2. Oriental “Sapphires.” These embrace 6 kinds. The blue Sapphire. ” red or “Ruby.” ” green or Emerald. ” purple or Amethyst. ” golden or Topaz. ” sea-green or Aquamarine. These are pure Alumina. “Emery” is a coarse variety of Corundum. “_Aluminates._” Of Magnesia { Spinel ruby. { Balas do. A Phosphate of Alumina and Magnesia } Turquoise.