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A REVIEW OF THE GENESIS OF THE ZEOLITE DE. POSITS OF FIRST WATCHUNG MOUNTAIN, N, J.1
Abstract
InrnorucrroN Nnw Jnnsny is fortunate in having many famous mineral localities, and of these perhaps the most frequently visited by collectors are the trap quarries of First Watchung Mountain, especially thbse at West Paterson and Great Notch. These occurrences have also received considerable attention from investigators, but the conclusions rvhich have been arrived at as to the genesis of the minerals are not in general familiar to collectors. This is particularly true concerning some of the more recent discoveries, and the present paper has been written to call attention to these discoveries and the resulting conclusions as to the genesis of these remarkable mineral deposits. Gnor,ocy2 The rocks of this region are of Triassic age and consist of sedimentary rocks with interbedded basalt flows, the whole collectively known as the Newark Group. The sedimentaries comprise fine-grained red shale, sandstone, conglomerate, and dark colored argillite or mudstone; the source of the materials having evidently been the gneiss, quartzite and limestone of the Highland belt to the west. Ripple-marks, mud- cracks, rain-drop impressions, foot-prints of reptiles, and mineral cavities are frequently found. These sedimentaries are now be- lieved to be of continental origin, deposited under semi-arid conditions in basins at the foot of the then newly uplifted Appa- lachian Mountains.
... Varieties of quartz reported from the Newark basin in New Jersey include amethyst, smoky quartz, clear quartz crystals, palecolored chalcedony, and agate in the Jurassic basalt formations [11], and amethyst, milky quartz, clear quartz crystals, pale-colored chalcedony, and opal in Jurassic diabase and references therein [12]. No reference is made to carnelian or other synonymous names such as cornelian, red chalcedony, or sard in any of the New Jersey mineral inventories [13][14][15] or studies on the occurrence and diversity of zeolites and associated secondary minerals in basalt and diabase in the Newark basin [11,12,[16][17][18][19][20][21]. ...
... Oxygen isotope analyses of carnelian samples yield high δ 18 O VSMOW values that range from +18.3 to +31.2‰ (Table 4), with all but one sample having an δ 18 O of +27.9 to +31.2‰. The analytical precision (1σ) is ±0.06‰ in two samples and ±0.21 to 0.64‰ in the other four (Table 4)O compared to ±0.1‰ for the standards, indicating isotopic heterogeneity, particularly in GBR-3 and GBR-4. ...
Carnelian occurs locally in New Jersey in the Newark basin as medium- to coarse-size pebbles in fluvial gravel and alluvium and colluvium formed from erosion of Lower Jurassic Preakness Basalt. Vesicles and molds of glauberite are preserved on lower surfaces and botryoidal textures on the upper surfaces of some pieces. The microstructure consists of length-fast chalcedony characterized by parallel fibrous bundles overlain by repetitive, wavy extinction bands. Only peaks of ɑ-quartz and minor moganite are recognized in X-ray diffraction patterns. Carnelian contains 97–98 wt.% SiO2, ~1.0 wt.% Fe2O3, and 1.0–1.4 wt.% LOI; other major elements are <0.1 wt.%. Trace element abundances are low except for Y, Nb, Ta, W, Th, and U. Rare earth element (REE) patterns display heavy REE enrichment and large negative Eu anomalies. Most trace elements were mobilized from Proterozoic sources, whereas Si was likely derived from the alteration of basaltic glass in the Preakness. Carnelian δ18OVSMOW values are high and range from +18.3 to +31.2‰, comparable to global occurrences of volcanic rock-derived chalcedony. We propose that carnelian precipitated in the first Preakness flow from the mixing of hydrothermal fluid with meteoric water under conditions of low temperature (20–80 °C) and neutral to slightly alkaline pH.
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