. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 412 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES comparable with that of idocrase. There is also a certain similarity between idocrase and other green stones, such as diopside, epidote, demantoid, &c.: the methods by which these may be distinguished are given in the third part of this book (Tables 13 and 14). The idocrase of Vesuvius is found, tog
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 412 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES comparable with that of idocrase. There is also a certain similarity between idocrase and other green stones, such as diopside, epidote, demantoid, &c.: the methods by which these may be distinguished are given in the third part of this book (Tables 13 and 14). The idocrase of Vesuvius is found, together with other beautifully crystallised minerals, in the limestone blocks ejected from the old crater of Vesuvius, now represented by Monte Somma. The crystals are attached to the walls of cavities in this metamorphosed limestone, And range in colour from darkest brown to honey-yellow. A cut stone of brown idocrase from Vesuvius is represented in Plate XV., Fig. 3. Some of the pale brown stones found here are much admired ; they are not unlike hyacinth (zircon) in colour, and, indeed, are sometimes mistaken for that stone. There is no difficulty, however, in distinguishing between the two minerals, owing to the density of zircon being so much greater than that of idocrase. The methods by which idocrase may be distinguished from other brown stones, such as smoky-quartz, brown tourmaline, axinite, &c., are given later (Tables 9 and 11). The mineral known as xanthite and found at Amity, in Orange County, New York, is nothing more than dark yellowish-brown idocrase; it is sometimes cut as a gem, but is worn only in the United States. For both green and brown idocrase the step-cut or the table cut is employed ; other forms are scarcely ever adopted. In correlation with the limited demand for idocrase as a ^em, we find that both for brown and for green stones quite low prices are AXINITE. In just a few cases transparent crystals of axinite are cut as gems, usually en ca
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