glass-gall

“The fibres of the pumice-stone of the Peak are very seldom parallel to each other, and perpendicular to the strata of obsidian; they are most commonly irregular, asbestoidal, like fibrous glass-gall; and instead of being disseminated in the obsidian, like crystalites, they are found simply adhering to one of the external surfaces of this substance.”

Personal Narrative of Travels to the Equinoctial Regions of America, During the Year 1799-1804 — Volume 1

“Some of these sink to the bottom, and some rise in scum, or, as it is called here, glass-gall, and sometimes sandiver. ”

The Atlantic Monthly, Volume 14, No. 83, September, 1864