Beach Rambles in Search of Seaside Pebbles and Crystals / With Some Observations on the Origin of the Diamond and Other Precious Stones

by John George Francis

Opal is a “hydrate” of Silica, containing 7 per cent. of water.

• Precious, or “noble.”
• Iridescent.
• Common (colourless).

“Silicates.”

Of Alumina	Feldspar.
	Kaolin.
Of do. with Glucina	Emerald.
	Beryl
	Garnet
	Pyrope, or “precious garnet.”
Of Magnesia	Chrysolite.
	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.”