Physical Characteristics and Composition of Jaspers

JASPER:

The precious jasper is the jaspeh of Aaron's breastplate; the iaspis of the Greeks.

"The property which distinguishes jasper from other varieties of quartz is its complete opacity even in thin flakes. Jasper is often a silex that has become opaque either by alteration that it has undergone, or by the addition of a certain quantity of oxide of iron, or of hydrate of the same oxide. There are red jaspers, brown jaspers, and green jaspers. In certain circumstances, as in the Egyptian pebble, the jasper presents irregular zones, which display a structure roughly concentric" (Dufrenoy).

It is one of the thousand varieties of rocks known under the name of jaspers. These varieties, hard enough to cut glass, present wide bands of diverse colours, generally red and green, upon a brown ground.

The silicious element predominates in the jaspers, but with it is associated certain bases (alumina, oxide of iron, &c.), sufficient to render the whole fusible under the flame of the ordinary blowpipe, which is not the case with quartz or its varieties that are very nearly pure.