Jasper

Jasper (Gr. iaspis), a mineral generally regarded as one of the varieties of Quartz (q.v.), and distinguished by its opacity, owing to a mixture of clay or other substances with the silica of which it is chiefly composed. There are many kinds of jasper, some of them of one colour, as brown, red, yellow, green, white, blue, or black, and some variously striped, spotted, or clouded with different colours. Jasper is a very abundant mineral; it is found in veins and embedded masses in many rocks, sometimes appears as a rock of which whole hills are formed, and is very common in the shape of pebbles. It has been prized from the most ancient times for ornamental purposes, as it takes a high polish. The kind called Porcelain jasper is rather rare. It is often full of minute holes, or is cracked in all directions. It is regarded as a kind of natural porcelain, and is found in places where coal-seams have taken fire: it is thus simply a baked clay. Similar baked clays are not infrequently met with in the vicinity of intrusive igneous rocks.