About SemiPrecious Stones: Obsidian, Phenacite, Pyrite, and Rutile

THE mineral world contains many beautiful materials that are without the pale which encloses the clearly defined gem stones; these "outlanders" may be classed as semi-precious stones that are only occasionally used, and while many are truly beautiful and others are interesting, because of rarity or peculiarities, all lack some quality--usually a sufficient degree of hardness--which would admit them into the patrician rank of Precious Stones. Because of their intense scientific interest, technical mineralogists, who have written books about gems, not only include but devote considerable space to minerals that will not meet the eye of one manufacturing jeweller or gem dealer in one hundred, or ever be seen by one gem buyer in thousands. These stones are usually not so rare in nature as they are in stores, and their cutting and mounting is usually the result of an individual order; otherwise they are collected and cut only for collector's specimens. Brief mention will be here given to some of the minerals that occasionally appear and are included in the stocks of the principal stone merchants. In the American market there is a difference in this respect between the market east of the Pacific coast cities and localities near them or close to the Rocky Mountains and the Sierras, because that mountainous region is a great mineral treasure house, yielding many welcome finds of attractive and beautiful semi-precious stones; therefore in San Francisco, Denver, and other Western cities, these local minerals are used in jewelry to a greater extent than they are in the midland cities and those of the Eastern States.

Among the stones most likely to appear from time to time in the shops are:

OBSIDIAN is compact volcanic glass, and is cut for gem purposes to a greater extent than some of the other semi-precious stones here referred to. Varieties are moldavite, or bottle stone, of a green colour; marekanite or mountain mahogany, a red or black and brown banded kind; and Iceland agate; pearlylite; and sphaerulite.

PHENACITE, of gem quality, is transparent, colourless, and of a vitreous lustre. This brilliant mineral is harder, heavier, and more refractive than quartz, which it so closely resembles, so that it was not until 1833 that mineralogists differentiated between them. Its name, phenacite, is derived from the Greek word phenax, meaning a deceiver. Phenacite remotely resembles the diamond in its brilliancy and refractiveness. Some specimens exhibit pale-rose and wine-yellow colours.

PYRITE is a brass-yellow mineral of metallic lustre known to jewellers as sulphur-stone and technically as marcasite. It is a common mineral, and is so frequently mistaken by the uninformed for gold that it has earned the sobriquet "fool's gold." Pyrite is a sulphide of iron. Although so common as to have no intrinsic value, pyrite constantly remains in use in jewelry and is seen in rings, brooches, and scarf pins. In coal-mining regions it is sold as souvenirs, mounted in medium to low-priced settings.