Etymology
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quartz (n.)

common form of native silica or silicon dioxide, 1756, from German Quarz, Zwarc "rock crystal," from Middle High German twarc, probably from a West Slavic source, compare Czech tvrdy, Polish twardy "quartz," noun uses of an adjective meaning "hard," from Old Church Slavonic tvrudu "hard," from Proto-Slavic *tvrd-, from PIE *(s)twer- "to grasp, hold; hard."

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quartzite (n.)

"rock composed essentially of the mineral quartz," 1837, from quartz + -ite.

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chert (n.)
"flint-like quartz," 1670s, of unknown origin. Apparently "a local term, which has been taken into geological use" [OED].
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touchstone (n.)
late 15c., from touch (v.) in the Middle English sense "to test" (metal) + stone (n.). Fine-grained black quartz, used for testing the quality of gold and silver alloys by the color of the streak made by rubbing them on it. Also see basalt. Figurative sense is from 1530s.
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chalcedony (n.)

semi-precious stone, a cloudy white variety of quartz, c. 1300, from Latin calcedonius, a Vulgate rendering of Greek khalkedon in Revelation xxi.19; found nowhere else. "The word is of very complicated history" [OED]. Connection with Chalcedon in Asia Minor "is very doubtful" [OED].

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opal (n.)

"mineral like quartz but without crystalline structure," 1590s, from French opalle (16c.) and directly from Late Latin opalus (Pliny), supposedly from Greek opallios, which is possibly ultimately from Sanskrit upala-s "gem, precious stone." Used in Middle English in Latin form (late 14c.). Related: Opaline.

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mother lode 

"important vein of an ore or mineral in rock," 1849, from mother (n.1) + lode (n.); said to be a translation of Mexican Spanish veta madre, a name given to rich silver veins. The American use is first in reference to a conspicuous vein of quartz rich in gold discovered during the gold rush in the Sierra Nevada of California. The colloquial or figurative sense of "richest source of something" is by 1916.

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onyx (n.)

type of quartz characterized by a structure in parallel bands differing in color or degree of translucency, used for cameos, etc., mid-13c., oneche; c. 1300, onix, from Old French oniche "onyx" (12c.), and directly from Latin onyx (genitive onychis), from Greek onyx "onyx-stone," originally "claw, talon, hoof, fingernail" (see nail (n.)). So called because the mineral's color sometimes resembles that of a human fingernail, pink with white streaks.

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paste (n.)

c. 1300 (mid-12c. as a surname), "dough for the making of bread or pastry," from Old French paste "dough, pastry" (13c., Modern French pâte), from Late Latin pasta "dough, pastry cake, paste" (see pasta). Meaning "glue mixture, dough used as a plaster seal" is attested from c. 1400; broader sense of "a composition just moist enough to be soft without liquefying" is by c. 1600. In reference to a kind of heavy glass made of ground quartz, etc., often used to imitate gems, by 1660s.

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agate (n.)
variety of banded, colored quartz, 1560s, from French agate, from Latin achates, from Greek akhates, the name of a river in Sicily where the stones were found (Pliny). But the river could as easily be named for the stone.

Earlier in English as achate (early 13c.), directly from Latin. The Elizabethan sense of "a diminutive person" is from the small figures cut in agates for seals, etc., and the notion of smallness is preserved in typographer's agate (1838), the U.S. name of the 5.5-point font called in Great Britain ruby. Meaning "toy marble made of glass resembling agate" is from 1843 (colloquially called an aggie). Related: Agatine.
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