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APOPHYLLITE

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

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

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

light, a See also:peculiar interference figure, the rings being alternately white and See also:violet-See also: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 See also:basalt and melaphyre. Magnificent See also:groups of greenish and colourless See also:tabular crystals, the crystals several inches across, were found, with flesh-red stilbite, in the See also:Deccan traps of the Western See also:Ghats, near Bombay, during the construction of the See also:Great See also:Indian See also:Peninsular railway. Groups of crystals of a beautiful See also:pink See also:colour have been found in the See also:silver See also:veins of Andreasberg in the Harz and of Guanaxuato in See also:Mexico. Crystals of See also:recent formation have been detected in the See also:Roman remains at the hot springs of Plombieres in See also:France. (L. J.

End of Article: APOPHYLLITE

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APOPHYSIS (Gr. amrocvves, offshoot)

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