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Volume 82, 1954-55
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b. Significance

Authigenic analcime has often been reported in pyroclastic rocks. Thus Tyrrell and Peacock (1926) describe an Icelandic occurrence of analcime which is associated with faujasite, a potassium analogue of analcime and limonitic or chloritic material together representing joint alteration products of palagonite tuff.

In the Great Geyser Basin bore-hole of Yellowstone described by Fenner (1936), analcime occurs with quartz and adularia in dacitic gravels and sands altered by alkaline, hot-spring activity in the depth range 86 to 216 feet. This corresponds with a present-day temperature of 125–157° C. and is just below the zone in which heulandite appears.

Bradley (1928, 1929) has described widespread beds containing as much as 65% analcime extending over many hundreds of square miles in two separate intermontane basins of the Eocene Green River formation of Utah, Colorado and Wyoming. He showed convincingly that the analcime was formed by reaction and replacement penecontemporaneously with deposition of ash in saline lakes. Hydrothermal action was in no way responsible. Salt crystal moulds in near-by

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Fig. 1.—North Range (2,120 feet) showing hog-back ridges of resistant Lower to Middle Triassic meta-andesitic tuffs It is separated by a broad belt of siltstones from white Hill (Kaihikuan and higher stages) to the left View looking N. N. W.
Fig. 2.—Spheroidal quartz-albite-adularia metasomatite showing concentric veining, in laumontitized tuff Bed NR2 North Range.
Fig. 3.—Steeply dipping bed of laumontitized ash 10 feet thick. with detached joint blocks littering slope to the right NR5, North Range.

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Fig. 1.—Granular mosaic of quartz (low relief) replacing laumontite (strong negative relief and good cleavage) 8784. NR5,, North Range Ordinary light, X150.
Fig. 2.—Aggregate of pumpellyite (dark grey) in metasomatite Secondary quartz (colourless) and feldspars (light grey) preserve ghost-like traces of ash structure 8818, NR2,, North Range Ordinary light, X100.
Fig. 3.—Icositetrahedral pseudomorphs of feldspars after analcime set in quartz 8824, NR2,, North Range Ordinary light, X100.
Fig. 4.—Contact between laumontitized tuff (light) and quartz-albite-adularia metasomatite (dark) Dark streaks of quartz and adularia occur in laumontite near the contact and roughly parallel to it 8799, NR2,, North Range Almost natural size.

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Fig. 1.—Tuffaceous greywache Meta-anlesitic rock debris and loose crystals of albitized plagroclase and rarer augite in a base rich in chlorite and leucovene 8932 NR3,, North Range Ordinary light, X29.
Fig. 2.—Fine rhvodacite vitric tuff Small cuspate glass particles have devitrified to heulandite. often darkened with non oxides A large clear crystal of andesine is near the top and smaller fragments are in the groundmass 9035. 100 feet below top of Oretran Wether Hill Ordinary light, X23.
Fig. 3.—Quartz-albite adularia metasomatite showing some large lapilli (dark) cut by anastomosing veinlets secondary feldspar NR2, North Range X4/3.
Fig. 4.—Felt of secondary albite in metasomatite, with a few large albitized plagioclase fragments 8814. NR2, North Range Crossed nicols. X90.

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beds prove the high salinity of the lake waters. Similarly, Ross (1928, 1941) has described a bed of “sedimentary analcite” from West Yavapai county, Arizona, formed where tuffs have fallen into and reacted with saline playa lake waters.

Rengarten (1940) has found authigenic analcime deposited around fragments of decomposed porphyrite in Permian sandstones from Russia and as minute crystals in the gypsum and carbonate matrix. It is considered to have been formed during the deposition of the sandstone and the evidence of high salinity will again be noticed. Again, Keller (1952) considers that a zone of analcime-rock in Triassic mudstones in Wyoming is due to the action of strong saline solutions on clay, which was perhaps derived from volcanic tuff.

It seems clear that analcime may be formed by the attack of highly saline waters on volcanic glass at atmospheric temperatures. The Taringatura analcimized tuffs are interbedded with marine fossil bands. Evidence to show whether normal sea water at normal temperatures will bring about analcimization of glass is inconclusive, although Raw (1943) considered that analcime has been formed in palagonite tuffs from Jamaica by the action of salt sea water. On the other hand, the lime-rich zeolite phillipsite was found by the Challenger Expedition (Murray and Renard, 1891, pp. 400–412) to be widely distributed in deep-sea deposits and was apparently formed by reaction with basic glass at temperatures fluctuating 2–3° C above and below zero. Bramlette and Bradley (1940) also recorded phillipsite (?) rather than analcime in deep-sea cores from the floor of the North Atlantic.

It is believed that in the Taringatura sediments, analcime, like heulandite, has been formed from volcanic ash either penecontemporaneously with deposition or at moderate depths of burial, and that sea water or connate waters must have provided the additional sodium for its formation.

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