Which of These Rocks, Mostly from Glass Mountain, CA, Will Float

I've gathered up a collection of rocks to see which ones will float and which ones will sink. All but one of these are glassy volcanic rocks from Glass Mountain in northeastern California. The ones from Glass Mountain are all rhyolitic.

This test is a follow on to a short discussion in the comment section of a recent post, resulting in two questions we can ask about the six rocks I've set on an outdoor table in the backyard: Which of these rocks will float? And can we call any of these rocks pumice?

Rock #1: A scouring block of vesicular rhyolite (flow rock) from Glass Mountain. Rock collected by MOH.

Rock #2: A second scouring block from the same locality as Rock #1. Rock collected by myself.

Rock #3: I wouldn't hesitate to call this pumice. It's from the pumice pit at Glass Mountain (Google Maps location). Rock collected by MOH.

Rock #4: Banded rhyolite obsidian from Glass Mountain.
Rock collected by MOH.

Rock #5: Vesicular rhyolitic flow rock from Glass Mountain, with flow lineations on the upper surface. Rock collected by MOH.

Rock #6: Crenulated slaty phyllite from eastern Nevada.
Rock collected by myself.

I threw the last rock into the mix just to test something smallish and flat. Also, it's shaped somewhat like the state of Nevada, one of my favorite states.

Okay! Here we go! Any guesses?

Vote for your selection(s) in the comments.

Happy Holidays!

Xmas Eve greetings! Photos are all from Nevada City, CA, although I'm elsewhere at the moment. Above: the Outside Inn.

Inside the Mine Shaft.

Likewise.

Xmas cheer from inside Lefty's.

Finding a Thesis: Coming into Clayton Valley

On the road to Silver Peak from the east, about six or seven miles past Alkali and while one is still on pavement, Clayton Valley comes into view. The road turns to dirt—gravel and dust—not far beyond this first photo, and not far before the second.

Panoramic view of Clayton Valley in front of the eastern nose of Mineral Ridge.

The same photo, labelled.

In this view, we're looking at Mineral Ridge nearly end-on, essentially down the axis of the mountain-sized anticline that it is. Mineral Ridge, Red Mountain, and the ridgeline on the far left are all part of the greater Silver Peak Range. The ridge, with its high point of 9376 feet (2858 m), hides the range's high point, Piper Peak, and also blocks any view of the Mohawk and Sanger Mines beyond. The reddish brown, dome-shaped Red Mountain, composed of Tertiary rhyolite (Albers and Stewart, 1972), sits at 8957 feet (2730 m) just in front of and to the right of the unnamed ridge. Silver Peak itself is barely in the picture in the left side of the photo—you can see little hints of green if you look closely—just beyond the lithium brine fields of Clayton Valley. The low green slopes on the either side of the dirt road in the foreground consist of natural outcrops of olive to bluish-green shale of the Cambrian Harkless Formation. We'll see more of the cinder cone, The Crater, later in this Silver Peak portion of LFD's thesis-hunting series.

Labelled aerial view of the Clayton Valley–Silver Peak area, courtesy USGS (TNM Viewer link). The lithium brine fields are dead center. "You Are Here" marks the site of the previous photo.

Topographic map of the same view, courtesy USGA (TNM Viewer link).

Past the gap between the north end of Clayton Ridge and the south end of Paymaster Ridge, Silver Peak Road begins to cross the ever-changing lithium-brine fields and ponds. It turns out that there’s a more direct way to Silver Peak from the Palmetto Mountains on dirt via Oasis Divide (off the southwest edge of the map above), but fortunately I didn’t try it back in 1976. It’s a usually washboardy, tire-spinning, sandy road, with lots of inconvenient turns. I doubt the Opel would have made it.

So there I was, finally crossing the large, lithium-brine mining operations in Clayton Valley. (Photos are all from a photo-gathering expedition I made in the summer of 2010.)

Sign near the middle of the lithium brine fields.

The lithium operation, run by Chemetall Foote Corporation back in 2010 according to these signs, is now supposedly owned and run by Albemarle Corporation. Back in '76, it was run by Foote Mineral Company. (The brine mining operation has undergone several name changes over the years.)

More signs.

I'm not really sure what I thought of the lithium brine fields when I traversed the playa from east to west back in 1976, but I probably felt conspicuous and out-of-place. (This was a common feeling during my thesis-hunting adventures: An Opel was fairly uncommon vehicle overall and was even more uncommon off pavement, dirt roads and the Nevada outback were unfamiliar to me, and I was persistently plagued by the thought that I didn't know what I was doing.) Even now, making the crossing can seem a little strange to me, although I did become accustomed to going back and forth across the brine fields back in the mid-1980s when I worked on top of Mineral Ridge. What's odd about the crossing? It's unusual to find such a major dirt road traversing a playa, and what with the all the power and phone lines on both sides, the visual impression is unique. The traffic can be heavier than one usually finds on a playa (barring unexpectedly being on the Black Rock Desert during Burning Man), and one has to watch for trucks and construction equipment.

Silver Peak: about four more miles.

Off to the northwest, the dark prominence of The Crater, a basalt cinder cone, stands out above the salty desert floor.

And there we are: the south end of Silver Peak is to the right.

Read a little more about the brine fields here (USGS, basic info apparently from 1982, still relevant), here (the origin of the brine fields), and here.

Related Posts:
Thesis: Finding an Area
Finding a Thesis: Battle Mountain to Austin to Gabbs
Finding a Thesis: Pole Line Road
Finding a Thesis: Pole Line to Belmont
Finding a Thesis: Klondyke District
Finding a Thesis: A Joshua Tree Aside
Finding a Thesis: Into the Palmetto Mountains
Finding a Thesis: Farther into the Palmetto Mountains
Finding a Thesis: A Bit O' Geology in the Palmetto Mountains
Finding a Thesis: Future Stories from the Palmetto Mountains
Lida Summit Roadcut
Finding a Thesis: Next Stop, Silver Peak!

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?

Finding a Thesis: Next Stop, Silver Peak!

And so we say goodbye to the Palmetto Mountains.

In actuality, the picture above—taken as I was leaving the Lida-Palmetto area for Fish Lake Valley during my 2010 property-exam trip—has us looking in the rearview mirror at a mine dump located on the west side of the Palmetto Mountains, whereas in our continuing thesis-finding stories, I left the Palmetto Mountains to the east, via the same route I came in on. And so the intertwined 1976–2010 stories continue:

I wasn't too keen about spending another night in the Palmetto Mountains, and so, after duly looking around at a few prospects in the Palmetto mining district, I took my leave by descending the alluvial fan on the south side of the Palmetto Mountains. (In Google Earth, the southwest-facing slope actually looks like a complex of thinly veneered to dissected pediments with localized alluvial fans of more than one age.)  I might have stopped to look at the the ghost town of Palmetto, and I might not have.

After shooting past Lida, I eventually turned north on Highway 95, then turned west onto the Silver Peak Road a few miles north of Goldfield. I then made the relatively easy drive to Silver Peak, partly on pavement loaded with potholes and partly on dirt.

I would have barreled past Alkali and Alkali Hot Springs. Having never bathed there and having stopped only once or twice to look around, I don’t have any good digital pictures of the easily accessible but privately-owned spot.

The Silver Peak Road approaches Alkali from the east. We're looking at the Weepah Hills in the distance beyond the playa known as "Alkali Lake" (original, eh?), and beyond a low part of Paymaster Ridge. The Weepah Hills high point, on the right, is at 7753 feet.

About a half mile past Alkali Hot Springs, a major road junction is marked by a large rock (Google Maps location).

Large rock marking the junction of the paved road to Goldfield (the Silver Peak Road, which we've been on) and the graded gravel road to Tonopah.

Looking NE along the dirt road, back toward Tonopah and the Klondyke Hills.

The rock says, Tonopah: 24 miles.

Looking SE along the paved road back toward Alkali Hot Springs and Goldfield, the latter of which is not visible beyond the horizon. The hazy hills behind the rock are volcanic-capped bluffs in the Goldfield Hills north of Goldfield.

The rock says, Goldfield: 7 miles.

The rock looks volcanic to me; it could possibly warrant further scrutiny, but I've always looked at it as an interesting road artifact. (I've never taken my hammer to it: Heaven forbid!)

Looking WSW from the site of the rock-sign, toward Silver Peak. The south end of Paymaster Ridge blocks the view of all but the highest peaks of the Silver Peak Range miles beyond.

From Alkali, I pushed on to the next stop on my list, the Mary Mine, which is perched near the top of Mineral Ridge, an elongate, nearly oval mountain with the small town of Silver Peak at its eastern extremity. Mineral Ridge proper lies between Silver Peak and Rhyolite Ridge, all technically part of the Silver Peak Range.

Topo map courtesy USGS (TNM link).

Silver Peak is called Silverpeak on this map, as it is on some and not on others. The Board of Geographic Names is now favoring Silver Peak, after naming decisions in 1965 and 1987, so Silver Peak was most correctly known as "Silverpeak" from 1965 to 1987—including when I was there in 1976—and that's probably why some road signs still say "Silverpeak." I also should also have been using the one-word version of the name when I was there in the mid-1980s, but I wasn't. By then, almost no one was (citation: my memory of my own undocumented experience).

Related Posts:
Thesis: Finding an Area
Finding a Thesis: Battle Mountain to Austin to Gabbs
Finding a Thesis: Pole Line Road
Finding a Thesis: Pole Line to Belmont
Finding a Thesis: Klondyke District
Finding a Thesis: A Joshua Tree Aside
Finding a Thesis: Into the Palmetto Mountains
Finding a Thesis: Farther into the Palmetto Mountains
Finding a Thesis: A Bit O' Geology in the Palmetto Mountains
Finding a Thesis: Future Stories from the Palmetto Mountains
Lida Summit Roadcut [essentiall another aside]