. Pierres précieuses, un compte rendu populaire de leurs personnages, l'occurrence et d'applications, avec une introduction à leur détermination, pour les minéralogistes, lapidaires, bijoutiers, etc. avec un appendice sur les perles et le corail. Pierres précieuses ; Perles ; les coraux. 426 DESCRIPTION SYSTÉMATIQUE DES PIERRES spécialement aucune amende après polissage lustre ; son application comme une pierre d'ornement dépend, par conséquent, uniquement sur sa couleur, et la plus profonde et plus pure, cette couleur est le plus hautement prisé est la pierre. Cette fonction d'amazon-pierre est supposé par certains d'être en raison de la présence d'une petite quantité de cuivre

• Contributeur: Central Historic Books / Alamy Banque D'Images
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. 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. 426 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES no specially fine lustre after polishing; its application as an ornamental stone depends, therefore, solely upon its colour, and the deeper and purer this colour is the more highly is the stone prized. This feature of amazon-stone is supposed by some to be due to the presence of a small amount of copper, but according to other authorities it depends on the presence of organic matter. Amazon-stone is a potash-felspar. It is found in irregular masses as a constituent of granitic, syenitic, and similar rocks; also as regularly developed crystals, which may reach ^ length of 25 centimetres, in magnificent druses, in the crevices and fissures of rocks of the same kind. Fig. 1 of Plate XVI. illustrates the latter mode of occurrence, and a single crystal is represented in Fig. 81. The physical characters of amazon-stone are the same as those of other felspars. Its specific gravity, in correlation with the chemical composition, is some- what low, varying between 2'55 and ^'66. The name amazon-stone was first given in the middle of the eighteenth century to a green stone from the Amazon river in South America. It appears to be doubtful whether this was the same sub- stance as that to which the name now refers ; more probably it was nephrite, jadeite, or some other green mineral, for nothing is known at the present day of the occurrence of verdigris-green felspar in this Fig 81. Crystalline ⢠j^ j^ j^ ^ ^^ occur in the Ural Mountains; here it is torm or amazon-stone. o found in compact masses near Miask on the eastern side of Lake Ilmen as beautiful crystals associated with topaz and other minerals in granitic rocks. It was met with later at a few places in North America; of these o

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