Tuesday, December 15, 2015

Before We Hike Down Glass Mountain...Some Scouring Stones

Before we go ahead and hike back down from the rhyolite flow on Glass Mountain, take a look, once again, at this view to the south. In the shadows on the right, you can see some beams and timbers from 1930s to 1940s mining operations that produced scouring stones, blocks, or bricks. The trail down took us right past the remains of the old operation (or, possibly, a particular part of the operation: roads snake all across the rhyolite flow). We stopped to look, realizing that anything we might find would likely be rejects, not finished stones that didn't make it into haulage trucks. MOH and I duly grabbed a couple examples.
Scouring stone #1.
The scouring blocks were produced from pumice and vesiculated rhyolite near the top of the rhyolite flow. An old report (CDMG, 1957, p. 2) says:
This pumice occurs as the crust of an obsidian flow and forms jumbled masses of angular blocks associated with black obsidian and dark gray coarsely vesiculated obsidian. Choice pumice blocks are medium gray in color, commonly range in maximum dimension from 1 foot to 3 feet and are relatively free from hard, dense bands. The pumice is loaded into trucks by tractor elevators and hauled to a processing plant near Tulelake where they are cut into "Grillmaster" scouring bricks.
Here's an example of a scouring brick you can buy today.

And here's what scouring block #1 looks like from a couple different angles:
Flow foliation shows well on one of the smoothed surfaces.
As we'll see in the next two photos, we're actually looking at a combination of foliation and lineation on the side shown above.
On the top, here, and down the sides, we can see good flow lineation.
And looking end-on, we see a kind of pock-marked surface: We're looking straight down the flow-lineation tube-like structures. The lineation can be seen in some of the pockety holes.
Scouring stone #2.
A pockety end surface with lineation plus foliation on the other surfaces.
On this smoothed surface, some dark gray or black spots show what the rock might have looked like prior to strong vesiculation.
I'm wondering: Would both of these rocks qualify as pumice by the float-test method?

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