shale - teaching hand specimens of a hard gray Lower Cambrian shale from the Marble Mountains of California
This is the Latham Shale, famous as a source of trilobite specimens from quarries in the Marble Mountains of San Bernardino County, California. It varies in color from gray to grayish green. Those quarries are now in the Desert Trails National Monument and are closed to collecting. This material was collected in 2015.
Students should know the basic sedimentary rocks in order of increasing grain size, from mudstone and shale, siltstone, sandstone to conglomerate and coquina.
Shales differ from mudstones in that they are more compressed, form flat plates, and are less likely to disappear in a poof of dust when dropped by a student. This shale is fairly hard and should stand up to student examinations.
Some shales closely resemble slate, metamorphosed from shale. To distinguish a shale from a slate, the field test is to lick it. The shale will smell muddy. The slate won't. This shale passes the lick-and-sniff test and smells distinctly muddy.
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