. 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. QUARTZ WITH ENCLOSURES 489 QUARTZ WITH ENCLOSURES. We have already seen that quartz frequently encloses other minerals and foreign substances of various kinds. These enclosures may be present singly in comparatively small numbers or in such multitudes as to impart an apparently uniform colour to the quartz substance, as is the case \\'ith prase and
. 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. QUARTZ WITH ENCLOSURES 489 QUARTZ WITH ENCLOSURES. We have already seen that quartz frequently encloses other minerals and foreign substances of various kinds. These enclosures may be present singly in comparatively small numbers or in such multitudes as to impart an apparently uniform colour to the quartz substance, as is the case \\'ith prase and with sapphire-quartz just described. It is proposed to consider here those cases in which there are present single enclosm-es of a nature to contrast very markedly with the quartz in which they are embedded. It is obvious that enclosures in translucent or opaque quartz will be seen very indistinctly or not at all, so that it is only the enclosures in very transparent quartz which ^\ill engage our attention. On the other hand, the clearness with ^\hich enclosures in quai'tz are seen is not at all affected by the colour of the mineral, objects embedded in amethyst being quite as distinctly seen as those in rock-crystal. These two varieties of quartz are those which most commonly contain enclosures, the different kinds of which will be described below in some detail. Hair-stoue and Needle-stone.—These names are given to quartz with enclosures of isolated, needle-like or hair-like crystals of various substances, like that represented in Plate XVIII., Fig. 2, which encloses green needles of actinolite. In other cases the enclosures may be white fibres of asbestos, long, thin crystals of rutile ranging in colour from yellow to red and somewhat resembling straw in appearance, and so on. Quartz containing enclosures of this description is distinguished as needle-stone or as hair-stone according as the enclosed crystals approach more to the thickness and straightness of a needle, or
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