The Pebbles on the Beach by Clarence Ellis

Author:Clarence Ellis [Clarence Ellis]
Language: eng
Format: epub
ISBN: 9780571353590
Publisher: Faber & Faber
Published: 2018-12-11T16:00:00+00:00

Yet, so slight is the difference in composition between chalcedony and the poor, common flint that the latter may be said to be just an inferior form of it. It would be equally true to say that the other varieties of silica that we are about to examine differ only in very slight degree from chalcedony.

You must not expect to find good specimens of it without prolonged search, for it is considerably rarer than quartz. It originates from cavities in granite and other igneous rocks and sometimes in the Old Red Sandstones. Good specimens are found on the Scottish coast and on the eastern and southern coasts of England.

The remaining varieties of quartz that we shall look at resemble chalcedony so much in all but colour and surface form that they might well be, and often are, called varieties of chalcedony. They are Agate, Onyx, Carnelian and Sard. All, like chalcedony, are non-crystalline and translucent forms of quartz. The cut and polished pebbles are charming, but you should take only your best specimens to the lapidary, as they are all harder than the most highly tempered steel and put up a stiff resistance to his cutting apparatus.

Of the several kinds of Agate (Latin: Achates, a river in Sicily), we can give our attention to the three that are the choicest and most striking.

Banded or striped agate is so called because its cut surface exhibits a succession of curved bands, stripes or layers, each band differing in colour from its neighbours. The curves are very roughly concentric and all of them are parallel to one another. Below is a simple plan of the structure of banded agate on the cut surface of a pebble.

FIGURE 10

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