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Rock Crystal

In response to a question from Epecho...

Rock crystal is synonymous with clear and colorless quartz. These days, it is most used in ornamental carvings, and best known as the substance out of which crystal balls are made. Although rock crystal is common, it's difficult to find it of the size and clarity needed to make something as large as a crystal ball. (Source: Rock Crystal entry in the Amethyst Galleries)

Eyeglasses were first made in the mid-13th century, out of rock crystal, although lenses had been used to help improve eyesight since at least a few hundred years earlier. While there is evidence for lenses from Greek, Roman, and Babylonian sources (the last being archaeological evidence), the only known use for them was filtering light or for burning holes into things, or cauterizing wounds. The University of Tennesee hosts a decent summary of the history of spectacles, although there are many, many others available online in addition to this one.

According to the OED, the first known use of the phrase "rock crystal" in English was in the 1666 Transactions of the Royal Philosophical Society (I.362), wherein a writer grumbled that "Rock-Crystal is not fit for Optick-Glasses." Although glass, replacing rock crystal, did indeed become the cheap and widespread material from which lenses were ground, certainly by the mid-15th century, it was not until the end of the 18th century that glass was made especially for the making of glasses. Up until that point, the glass ground into lenses was taken from byproducts of other parts of the glass-making industry.


( 4 comments — Leave a comment )
Feb. 22nd, 2003 09:48 pm (UTC)
Thanks Shana!

So rock crystal is the same as Quartz? Makes sense.

But when people refer to "crystal" products, such as (drinking) glasses, are they talking about rock crystal? I notice people talking about *lead* crystal glasses (for example http://groups.google.ca/groups?q=g:thl1974828450d&dq=&hl=en&lr=&ie=UTF-8&selm=37ADF142.F0575E6%40janics.com ). Is that different from rock crystal? And how so? Can lead really form crystal? From what I gather, crystal seems to be higher quality from ordinary glass. But I'm not sure whether that's rock crystal or lead crystal.

--Erik Stewart (possum@n-space.org)
Feb. 24th, 2003 04:08 pm (UTC)
Rock crystal, continued
Lead isn't nearly as exciting as you would like to think, unforortunately. Lead crystal is glass with high lead content, which causes it to form particularly clear and transparent crystal. So no, lead does not form crystals, but in compound with glass, it helps prettify the glass.

Crystal is a misleading term - without any adjectives, you have no way of knowing if it's quartz, glass, or, in fact, any other mineral or substantance which has crystalized.
Feb. 24th, 2003 04:03 pm (UTC)
I don't in fact recall asking that..
Regardless, though, I'm glad you answered it, because that's quite cool. It reminds me of the explanation of Iceland Spar in books about rocks when I was little; I never have actually laid my hands on a piece of the stuff. This (http://www.gemhut.com/calcite.htm) asserts that it was used in the bombsights (well, it says 'bombsites' in the text, but that would be a much different claim to fame) of bombers in WW2. And for only $25 US, they will ship me one and recapture my lost childhood. Good old Internet. I don't think so, though.

-Epecho (epecho.blogspot.com)
Feb. 24th, 2003 04:16 pm (UTC)
Iceland Spar
I've seen Iceland Spar in class and in museums - it's very pretty stuff, and does have strange optical properties. Since I was just playing with the dictionary, I noticed that "Iceland crystal" was the old name for Iceland Spar, and was, in fact, used to refer to it from around the year 1000 to the mid-nineteenth century. I don't know when the term Iceland Spar replaced it - could well have predated the last listed mid-19th century use.

The OED notes, to explain the use of the word crystal: "By the ancients and in the Middle Ages (rock-)crystal was supposed to be congealed water or ice `petrified' by some long-continued natural process. There was thus no transfer of sense in applying to it the same name as to clear ice, of which it was viewed as merely another state."

A spar is "a general term for a number of crystalline minerals more or less lustrous in appearance and admitting of easy cleavage." (OED again)
( 4 comments — Leave a comment )