• Webster's Revised Unabridged Dictionary
    • Toadstone (Min) A local name for the igneous rocks of Derbyshire, England; -- said by some to be derived from the German todter stein, meaning dead stone, that is, stone which contains no ores.
    • Toadstone Bufonite, formerly regarded as a precious stone, and worn as a jewel. See Bufonite.
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Century Dictionary and Cyclopedia
    • n toadstone Any one of various natural or artificial objects resembling a toad in form or color, or which were believed to have been formed within the body of that animal, and which for many centuries, and over a large part of Europe, were held in high regard, and preserved with the greatest care. ; The earliest reference to objects of this kind is that of Pliny, who, under the name of “batrachites,” described various stones which were said by him to resemble the frog in color, although he does not speak of their being possessed of any special virtues. This is the only reference to the toadstone to be found in classic authors; but much later on the names “crapodinus” and “bufonites” are found in various learned works written in Latin; while the word “crapaudine” appears in French as early as the fourteenth century, and “krottenstein,” “cradenstein,” and “krötenstein” not much later in German. Albertus Magnus and others also gave the name of “borax” to a stone supposed by them to be found in the head of the toad. This latter was the most common form of belief in regard to the origin of the toadstone, and it was very generally thought that it was endowed with special virtues if the animal could be made to surrender it voluntarily, Toadstones were preserved at the shrines of saints, worn as amulets, or set in rings, or in other ways treasured by their owners as charms, or antidotes to poison, or as having special therapeutic qualities, or simply as natural curiosities. Some of these objects were bits of rock, or of jasper, or of other semi-precious or perhaps really precious stones, toad-like in color or shape; others were fossils of various kinds, such as brachiopods, fragments of crinoids, teeth of fossil fish, etc.; in regard to many of them, however, no reasonable guess can be made as to their real nature, Shakspere refers to the toadstone in the lines
    • n toadstone In geology, a volcanic rock varying in texture from a soft crumbly ash to a hard close-grained greenstone, several beds of which occur in the magnesian limestone of the lead-mining district of Derbyshire The toadstone has the position of an interbedded rock, is irregular in thickness, and traversed by numerous veins and faults. It much resembles the so-called whinsill of Yorkshire, Durham, and Northumberland. Also called toadrock.
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In literature:

Last of all he showed me a toadstone amulet set in silver, a charm to prevent and ward off the spells of fairies.
"The Heather-Moon" by C. N. Williamson and A. M. Williamson
Popular names for them are "whinstone," "greenstone," "toadstone" and "trap.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 3" by Various