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slate - teaching hand specimen of black Jurassic slate from the core of the Santa Monica Mountains

$ 7.50

This Jurassic slate forms the core of the Santa Monica Mountains. It is well exposed at Point Mugu in Ventura County, California. Deposited in a remnant ocean basin during the Jurassic, it is dated using strontium isotopes at 163 + 14 million years (Medial Jurassic). Paleontologically, fossils of Buchia concentrica give a relative date of Late Jurassic (ca. 150 million years). 

There is a sequence of increasing compaction from sedimentary mudstone and shale to metamorphic slate. Shales are somewhat compressed and can resemble slates, as they both originated as fine-grained muddy sediments. A shale will often smell strongly muddy when licked. A slate, metamorphosed from shale by greater compaction and/or heating, will either not smell muddy, or will only smell slightly muddy when licked, a good field identification. This slate passes the sniff test, with a faint or no muddy smell when wetted, though it varies. Slate often can be parted in large smooth-surfaced sheets. Black slate used as the chalkboard in schools is the origin of the term blackboard.




This slate has been saw-trimmed on one or two or three sides to eliminate sharp edges and to fit into a 3 3/4" x 5 1/4" unit tray. It ships in a small flat rate box unless combined with other purchases. Click > About Shipping < for shipping rates. Use back button to return to this page. 

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