from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Any of various volcanic glasses distinguished by their dull pitchlike luster.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. a natural glass, that is rich in microscopic crystallites, formed by the rapid cooling of lava or magma
from the GNU version of the Collaborative International Dictionary of English
- n. An igneous rock of semiglassy nature, having a luster like pitch.
from The Century Dictionary and Cyclopedia
- n. An old volcanic rock, resembling hardened pitch in appearance.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. dark acid granitic glass
Most of our ground sits beneath the shadow of An Sgurr, a 1,289ft solidified lump of pitchstone lava.
The aggregates of globular bodies seen in the section so greatly resemble the globulites of slags and natural glasses, and in their arrangement so forcibly recall the structures seen in the well known pitchstone of
Sardara, Ploaghe, and other places; and considerable extents of trap and pitchstone are frequently met with on limestone strata, while others, tending fast to decomposition, are incorporated with an earth formed of comminuted lava.
Their flanks were blotched with a livid nitrous efflorescence, with flaring sulphur, unhealthy verdure of pitchstone, streaks of arsenical vermilion; their beds -- a frantic maze of boulders.
The whole northern and lower portion of the island had vanished, except an isolated pitchstone rock, ten yards square, and projecting out of the ocean with deep water all around it.
I even thought, with many other geologists, that obsidian, so far from being vitrified lava, belonged to rocks that were not volcanic; and that the fire, forcing its way through the basalts, the green-stone rocks, the phonolites, and the porphyries with bases of pitchstone and obsidian, the lavas and pumice-stone were no other than these same rocks altered by the action of the volcanoes.
When the basis of the lavas of the Malpays changes from pitchstone to obsidian, its colour is paler, and is mixed with grey; in this case, the feldspar passes by imperceptible gradations from the common to the vitreous.
We were stopped by a small circular wall of porphyritic lava, with a base of pitchstone, which concealed from us the view of the crater.
I strongly suspect the underlying granite has altered such beds into this pitchstone.
The lavas are curious from abounding in, or rather being in parts composed of pitchstone.