A translucent to transparent milky or grayish quartz with distinctive microscopic crystals arranged in slender fibers in parallel bands.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "chalcedony" in a sentence
"There is a kind of onyx called a chalcedony, which hath the same qualities,  avails much against fantastic illusions which proceed from melancholy, preserves the vigour and good estate of the whole body."
"As to the second, of which the name does not occur in treatises on gems, it may be identified with chalcedony, which is described as a sort of agate of an opaque quality, dimmed with clouds and flashing fires in the shadows."
"Of the seven necklaces pictured here, all purchased recently, three are varieties of chalcedony, which is itself a type of microcrystalline quartz."