Shorter contributions to general geology, 1929

Thin beds that consist almost wholly of euhedral analcite crystals occur at five or more horizons in the upper half of the Green River formation of Utah and Colorado, a series of Eocene lake beds that contain large deposits of oil shale. Most of these beds contain also minute crystals of apophyllite. The analcite crystals in some beds are cemented only by chalcedony, but in other beds that have less analcite the matrix is tuffaceous and consists of chalcedony in which are embedded splinters of feldspar, hornblende, and quartz, laths of biotite, and euhedral crystals of sanidine, apatite, and zircon. Analcite occurs plentifully also, disseminated in many of the oil-shale beds, and locally makes up as much as 16 per cent of weight of the rock. In these beds the analcite is accompanied by apophyllite, euhedral crystals of sanidine and orthoclase, angular fragments of quartz, and a little volcanic glass. The rocks associated with the beds of analcite and analcite-bearing oil shale contain salt-crystal cavities, that strongly suggest the former presence of glauberite and anhydrite.

Both clastic and hydrothermal hypotheses for the origin of the zeolites are considered and dismissed in the paper. The field and microscopic evidence presented leads to the conclusion that all the analcite and apophyllite formed in place on the lake bottom as a result of interactions between salts dissolved in the lake water and the dissolution products of volcanic ash that fell into the lake.

Meerschaum, or fibrous sepiolite, occurs in several thin beds near the top of the Green River formation in Duchesne County, Utah. It is mixed with structureless organic matter like that in the oil shale and apparently formed in place on the lake bottom.

Chemical analyses of the analcite rock and of the sepiolite are given.

Additional publication details
Publication type	Report
Publication Subtype	USGS Numbered Series
Title	Shorter contributions to general geology, 1929
Series title	Professional Paper
Series number	158
DOI	10.3133/pp158
Year Published	1930
Language	English
Publisher	U.S. Geological Survey
Description	iv, 173 p.
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