1 left

conglomerate derived from the Franciscan-Knoxville sequence - robust hand/display specimen

$ 12.50

The Mesozoic Franciscan-Knoxville sequence is a series of mostly metamorphic rocks characterized by serpentine, various cherts, shale and graywacke from which this conglomerate is derived. This accounts for the overall greenish hue of the clasts. "Clast" is derived from the Greek klastos, for broken, and refers to the rock fragments that make up sedimentary rocks.

This specimen was collected from the bed of Perkins Creek under the assumption that any conglomerate that had gotten that far would withstand student examination in a classroom. The source formation is uncertain.

The clasts in this conglomerate, originally loose pebbles in a stream channel, were stranded when the channel changed position, became buried, lithified into a conglomerate which was then uncovered, weathered and eroded. This chunk of conglomerate was then carried down the Perkins Creek drainage as a clast of conglomerate that is composed of smaller clasts, much like the flea having fleas. There is amazing variety in the rock types that make up this conglomerate. Many of the clasts are chert. Their angular nature indicates they were not carried very far before being trapped, buried and lithified to form this conglomerate.

Cut flat on both sides but not polished. Roughly 1 1/2" thick, so should be student resistant if it's not dropped.


Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil, a blue and silver pen, or one of those plus some number of coins, or you can let us make the selection.

Shipping: By Priority Mail. Click > here < for shipping rates. See comment at Note! Use back button to return to this page.

Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.