Online Encyclopedia

APOPHYLLITE

Online Encyclopedia
Originally appearing in Volume V02, Page 195 of the 1911 Encyclopedia Britannica.
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APOPHYLLITE  , a

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mineral often classed with the
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zeolites, since it behaves like these when heated before the
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blowpipe and has the same mode of occurrence; it differs, however, from' the zeolites proper in containing no aluminium . It is a hydrous potassium and calcium silicate, H7KCa4(Si02)s+44H20 . A small amount of fluorine is often
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present, and it is one of the few minerals in which ammonium has been detected . The temperature at which the
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water is expelled is higher than is usually the case with zeolites; none is given off below 2000, and only about
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half at 250°; this is slowly reabsorbed again from moist air, and is therefore regarded as water of crystallization, the remainder being water of constitution . When heated before the blowpipe, the mineral exfoliates, owing to loss of water, and on this account was named apophyllite by R . J. flatly in 1806, from the Greek afro, from, and OilMov, a leaf . Apophyllite always occurs as distinct crystals, which belong to the tetragdilal
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system . The form is either a square prism terminated by the basal planes (fig . 2), or an acute
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pyramid (fig . I) . A promi- nent feature of the mineral is its perfect basal cleavage, on which the lustre is markedly pearly, present-
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ing, in white crystals, some- what the appearance of the eye of a fish after The
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optical characters of the mineral are of
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special
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interest, and have been much studied . The sign of the double refraction may be either positive or negative, and some crystals are divided into optically biaxial sectors .

The variety known as leucocyclite shows, when examined in convergent polarized

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light, a
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peculiar interference figure, the rings being alternately white and
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violet-black and not coloured as in a normal figure seen in white light . Apophyllite is a mineral of secondary origin, commonly occurring, in association with other zeolites, in amygdaloidal cavities in
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basalt and melaphyre . Magnificent groups of greenish and colourless
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tabular crystals, the crystals several inches across, were found, with flesh-red stilbite, in the Deccan traps of the Western Ghats, near Bombay, during the construction of the
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Great
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Indian
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Peninsular railway . Groups of crystals of a beautiful
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pink colour have been found in the
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silver
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veins of Andreasberg in the Harz and of Guanaxuato in Mexico . Crystals of
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recent formation have been detected in the
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Roman remains at the hot springs of Plombieres in France . (L . J .

End of Article: APOPHYLLITE
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APOPHYGE (Gr. aaoda yit, a flying off)
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APOPHYSIS (Gr. amrocvves, offshoot)

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