The Conclusion of Our Float Test

We're about to test the rocks I posted about last week.

We have six float candidates (description here).

I voted for rocks #2 and #3 (as counted from the left in the photo shown above), with a "might" for #1 and "probably not" for #5. I did have the distinct advantage of being able to hold the specimens, thereby testing the heft

In comments, I got votes for:
1) Howard: none of the above
2) Lockwood: #3, with maybe but "I'd guess not" for #1 and #2
3) Ivar the Old: #3 (after thinking about #2 and then throwing it out)
4) Mathias: #3 and #2 (a "maybe" on the latter)

Rock #1. The larger of our two scrubbing stone rejects.

I wasn't sure if this rock would float: It has a lightweight heft for it's size, but I'm more used to feeling the heft of hand sized rocks, testing to see if a rock is limestone/dolomite v. barite, or limestone/dolomite v. fine-grained diopside skarn. I placed it carefully into the water, with one flat side down rather than end on into the water.

It's floating!

It's bubbling like crazy, and so I suspect the smallish vesicles will fill up with water, and when it gets completely waterlogged, it will likely sink (not a part of this test).

Rock #2: The smaller of our scrubbing stone rejects (remember, you can read more about these scrubbing stone rejects and see more detailed pics here).

I voted that this rock would float, although truth be told, the vesicle size is very similar to that of Rock #1 (so why didn't I vote for both of them?).

It's floating!

Possibly a higher percentage of the upper surface, compared to the upper surface of Rock #1, is sticking up above the water, but it's hard to judge the relative percentage of the entire rock in comparison with #1. And once again, I think it would probably become waterlogged eventually, and then it would sink.

I was sure that Rock #3 would float. It's a large piece of classic pumice.

Yep, there it is, floating. Most of the rock is sticking out above the water, almost the reverse of the previous two examples.

The pumice has small to very large vesicles.

Close-up of the largest of the air pockets or vesicles.

Overall, the pumice is quite frothy looking.

Rock #4, a piece of banded rhyolite glass.

I knew this rock would sink but included it in the test because it's composed of glass of about the same chemical composition as the glass in the previous three rocks.

It's on the bottom, no surprise.

Rock #5, vesicular rhyolite, also from Glass Mountain.

This is a large rock, lightweight for it's size, but it felt denser to me than the scrubbing stone rejects (Rocks #1 and #2) and doesn't look as vesicular. Consequently, I expected it to sink.

I placed it into the water with one of the flat sides down, and let go of it slowly.

It's definitely on the bottom.

Rock #6, a flattish piece of slaty phyllite.

I knew this rock (which is not a single large piece of mica) would sink, but I included it in order to a test of a rock with a different makeup than the other five. I also chose it for it's flat shape, to test whether the shape might make it float.

Nope. It's gone.

Three of five rhyolite samples from Glass Mountain floated and could therefore be called pumice. Their vesicularity, in order from most vesicular to least vesicular, is as follows: Rock #3, Rock #2, Rock #1, followed by Rock #5, which didn't float, and followed a long ways by Rock #4, which also didn't float. The difference between Rock #5, an example of vesicular rhyolite flow rock, and Rocks #1 and #2, pumiceous rhyolite flow rocks (the scrubbing stone rejects) is not great and might not be apparent when doing field work. Rock #4, which consists of dense, glassy banded rhyolite, is not vesicular at all. Rock #6, not a volcanic rock and not from Glass Mountain, also didn't float. It probably has a density similar to or slightly lower than the density of the dense rhyolite glass of Rock #4.

And that concludes our float test.