Tuesday, January 5, 2016

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.


Anonymous said...

I'll guess "none of the above"!


Lockwood said...

#3 looks like a probable "yes." 1 & 2, maybe, but I'd guess not. 4.5.6, no.

Anonymous said...

Even with specimen in hand estimating vesicle to matrix ratio dicey at best. In a photo? No way. However, guessing there might be a correlation between color and vesicle wall thickness I am left with #2 and #3. Since I can't resolve individual vesicle size on #2, I am left (assuming one actually floats) with #3.

Ivar the Old

Mathias said...

Ohhh...I go for #3 and maybe #2. The phyllite looks like a giant piece of mica. It is probably too big but small mica flakes can float on water - until you disturb it.

Silver Fox said...

I voted for #3, knowing for sure thay it would float, and also for #2, not being quite as sure. I figured #1 might float, and thought #5 probably wouldn't -- it felt pretty heavy and looked less vesiculated, but I thought I could be fooled by the size of it. Yes I had an advantage of being able to feel the heft.

For better look at the vesicularity, check out my earlier post about the scouring stones, #1 and #2.http://highway8a.blogspot.com/2015/12/before-we-hike-down-glass-mountainsome.html

I meant to link to that in this post.

Silver Fox said...

Scouring stone post