Encyclopædia Britannica, First Edition/Jasper

Jasper, in natural hiſtory, a genus of ſcrupi, of a complex irregular ſtructure, of great variety of colours, and emulating the appearance of the finer marbles, or ſemipellucid gems.

The great characteriſtic of jaſpers is, that they all readily ſtrike fire with ſteel, and make nor the leaſt efferveſcence with aquafortis.

Jaſpers, though commonly reckoned among the precious ſtones, ought undoubtedly to be ranged among the ſcrupi; being only opake cryſtalline maſſes, variouſly debaſed with an earthy admixture: and to this laſt ingredient it is that they owe all their variety of colours, as white, green, red, brown, and bluiſh.

The ſeveral kinds of nephritic ſtone, and the lapus divinus or jade, are all genuine jaſpers; but the hard, bright, green jaſper of the Eaſt Indies, ſeems to be the true kind. It is found in maſſes of various ſizes and shapes; but the more uſual ſtandard as to ſize, is between four and ſix inches in diameter; but there are maſſes of it found of a foot or more in diameter, and others no larger than a horſe bean. It is generally ſimple and unmixed; but if it be variegated at all, it is always with white; and this is diſpoſed not in ſtreaks or veins, but in clouds. It is capable of a very fine poliſh; and when the white clouds are well diſpoſed, is very beautiful; and, in pieces not too thick, is tolerably pellucid, when held up againſt the light.