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Dave, I can offer the explanations that follow:
John Sinkankas in Volume I of "Gemstones of North America," writes:
"An interesting mode of [obsidian] formation is represented by small
nodules of obsidian popularly called 'Apache tears.' These are found
in profusion in a number of the western United States and have a
curious geological history. It seems that some obsidian flows are
susceptible to alteration which proceeds rapidly along cracks and
fissures until the entire mass may, in time, be reduced to a puffy
porous rock called perlite. Because of the entrapped air, it is much
used for making light concretes and is also used as an insulating
material. In perlite, places are often found where alteration has
not reached everywhere and consequently small transparent glassy
nodules are discovered nestled in layers of the whitish porous
perlite."
Frederick Pough writes: "Old obsidian flows sometimes take up water
and change their glassy luster to a duller gleam. The moisture
trapped in this altered rock makes it swell up when it is heated, and
it turns into a glass froth, a sort of artificial pumice. This
man-made substance, sold as artificial "perlite," is in fact not
unlike natural pumice formed when a glass-filled mass of lava is
hurled from a volcano. The gas bubbles within the lava expand before
it freezes, to make the light glassy froth. Dull, partially altered
obsidian is known as pitchstone. Sometime a network of cracks
develops, etc., etc.).
So Apache tears are definitely obsidian, according to these two
world-renowned experts.
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