. 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. DIOPTASE 419 size and beauty as at the locality just mentioned. In America stones similar to those from the Knappenwand have been found at Rabun Gap, in Rabun County, Georgia; and fine dark green crystals have come from Roseville, in Sussex County, New Jersey, and from Haddam, in Connecticut; they are only occasionally, however, cut as gems. Again,
. 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. DIOPTASE 419 size and beauty as at the locality just mentioned. In America stones similar to those from the Knappenwand have been found at Rabun Gap, in Rabun County, Georgia; and fine dark green crystals have come from Roseville, in Sussex County, New Jersey, and from Haddam, in Connecticut; they are only occasionally, however, cut as gems. Again, a few crystals of green epidote are found with green tourmaline in Brazil. There must be many stones suitable for cutting to be found at the numerous loeahties for epidote, but since the use of this mineral as a gem is so limited and its value is so small, search for them is scarcely likely to be made. PIEDMONTITE. Piedmontite is a variety of epidote, in the composition of which alumina is replaced by manganese sesquioxide. This manganese-epidote is found principally in the manganese mines of San Marcello in the Piedmontese Alps, from whence the name piedmontite is derived. It sometimes occurs in magnificent cherry-red crystals, which, when they are of sufficient transparency, are cut as gems. DIOPTASE. Dioptase is a mineral of a deep green colour approaching, but always darker than, that of emerald. The two stones differ widely in chemical composition, however, for dioptase is a hydrous silicate of copper with the formula The results of an analysis of a crystal from the best and longest known locality, namely, that in Siberia, are given below: Per cent. 36-60 48-89 2-00 12-29 Silica (SiOa) . Cupric oxide (CuO). Ferrous oxide (FeO) Water (HjO) . 99-78 The green colour of dioptase is due to the large amount of copper which is present, and for the same reason the mineral is sometimes referred to as emerald- copper. Dioptase occurs usually in well-developed but smal
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